Cidara Therapeutics (CDTX) 10-K 25 Feb 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 18, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-36912
Entity Registrant Name	CIDARA THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-1537286
Entity Address, Address Line One	6310 Nancy Ridge Drive,
Entity Address, Address Line Two	Suite 101
Entity Address, City or Town	San Diego,
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	(858)
Local Phone Number	752-6170
Title of 12(b) Security	Common Stock, $.0001 Par Value
Trading Symbol	"CDTX"
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 151
Entity Common Stock, Shares Outstanding		48,043,143
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s definitive Proxy Statement to be filed with the Securities and Exchange Commission pursuant to Schedule 14A in connection with the registrant’s 2020 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K. Such definitive proxy statement will be filed with the Securities and Exchange Commission not later than 120 days following the end of the Registrant’s fiscal year ended December 31, 2020.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001610618

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 35,912	$ 50,268
Restricted cash	7,037	10,000
Accounts receivable	11,175	10
Prepaid expenses and other current assets	3,067	5,536
Total current assets	57,191	65,814
Property and equipment, net	342	429
Operating lease right-of-use asset	868	1,632
Other assets	2,023	1,101
Total assets	60,424	68,976
Current liabilities:
Accounts payable	4,568	1,887
Accrued liabilities	7,959	4,068
Accrued compensation and benefits	4,210	3,658
Current deferred revenue	13,865	9,803
Current portion of term loan	7,023	9,965
Current portion of lease liability	939	818
Total current liabilities	38,564	30,199
Lease liability	0	942
Long-term deferred revenue	11,145	0
Total liabilities	49,709	31,141
Commitments and contingencies
Stockholders' equity:
Common stock, $0.0001 par value; 200,000,000 shares authorized at December 31, 2020 and 2019; 44,876,408 shares issued and outstanding at December 31, 2020; 33,838,466 shares issued and outstanding at December 31, 2019	4	3
Additional paid-in capital	345,411	297,659
Accumulated deficit	(334,700)	(259,827)
Total stockholders' equity	10,715	37,835
Total liabilities and stockholders' equity	60,424	68,976
Series X Convertible Preferred Stock
Stockholders' equity:
Preferred stock, value, issued	$ 0	$ 0

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	44,876,408	33,838,466
Common stock, shares outstanding (in shares)	44,876,408	33,838,466
Series X Convertible Preferred Stock
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	1,096,519	565,231
Preferred stock, shares outstanding (in shares)	1,044,278	565,231

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Total revenues	$ 12,067	$ 20,915	$ 0
Operating expenses:
Research and development	68,017	46,401	49,142
General and administrative	15,899	16,238	14,143
Total operating expenses	83,916	62,639	63,285
Loss from operations	(71,849)	(41,724)	(63,285)
Other income (expense):
Change in fair value of contingent forward purchase obligation	0	411	3,851
Interest income (expense), net	(262)	221	629
Other expense	0	0	(211)
Total other income (expense)	(262)	632	4,269
Net loss	(72,111)	(41,092)	(59,016)
Recognition of beneficial conversion feature	(2,762)	0	(10,329)
Net loss attributable to common shareholders	$ (74,873)	$ (41,092)	$ (69,345)
Basic and diluted net loss per common share (USD per share)	$ (1.80)	$ (1.37)	$ (2.68)
Shares used to compute basic and diluted net loss per common share (in shares)	41,557,350	29,934,809	25,870,336
Unrealized gain on short-term investments	$ 0	$ 0	$ 8
Comprehensive loss	$ (72,111)	$ (41,092)	$ (59,008)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series X Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Other Comprehensive Loss	Registered Direct Offering	Registered Direct OfferingSeries X Convertible Preferred Stock	Registered Direct OfferingCommon Stock	Registered Direct OfferingAdditional Paid-In Capital	Stock Purchase Agreement	Stock Purchase AgreementCommon Stock	Stock Purchase AgreementAdditional Paid-In Capital	Controlled Equity Sales Agreement, Cantor Fitzgerald and Company	Controlled Equity Sales Agreement, Cantor Fitzgerald and CompanyCommon Stock	Controlled Equity Sales Agreement, Cantor Fitzgerald and CompanyAdditional Paid-In Capital	Rights Offering, January 2020	Rights Offering, January 2020Series X Convertible Preferred Stock	Rights Offering, January 2020Common Stock	Rights Offering, January 2020Additional Paid-In Capital
Balance, beginning (in shares) at Dec. 31, 2017		0	20,525,688
Balance, beginning at Dec. 31, 2017	$ 59,744		$ 2	$ 209,140	$ (149,390)	$ (8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (in shares)			847,937					445,231	6,185,987
Issuance of stock	6,440			6,440			$ 45,458		$ 1	$ 45,457
Recognition of beneficial conversion feature	0			10,329	(10,329)
Issuance of common stock for exercise of stock options (in shares)			89,031
Issuance of common stock for exercise of stock options	204			204
Issuance of common stock for restricted share units vested (in shares)			9,305
Issuance of common stock for restricted share units vested	21			21
Issuance of common stock under Employee Stock Purchase Plan (in shares)			158,066
Issuance of common stock under Employee Stock Purchase Plan	570			570
Stock-based compensation	5,710			5,710
Unrealized gain on marketable securities	8					8
Net loss	(59,016)				(59,016)
Balance, ending (in shares) at Dec. 31, 2018		445,231	27,816,014
Balance, ending at Dec. 31, 2018	59,139		$ 3	277,871	(218,735)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (in shares)												4,781,408			2,095,887
Issuance of stock											$ 9,008		$ 9,008	$ 5,289		$ 5,289
Issuance of common stock for exercise of stock options (in shares)			2,952
Issuance of common stock for exercise of stock options	$ 7			7
Issuance of common stock for restricted share units vested (in shares)	99,704
Issuance of common stock for restricted share units vested	$ 0			0
Issuance of common stock under Employee Stock Purchase Plan (in shares)			242,501
Issuance of common stock under Employee Stock Purchase Plan	411			411
Stock-based compensation	5,073			5,073
Unrealized gain on marketable securities	0
Net loss	(41,092)				(41,092)
Issuance of Series X Convertible Preferred Stock in exchange for common stock (in shares)		120,000	(1,200,000)
Issuance of Series X Convertible Preferred Stock in exchange for common stock	0
Balance, ending (in shares) at Dec. 31, 2019		565,231	33,838,466
Balance, ending at Dec. 31, 2019	37,835		$ 3	297,659	(259,827)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (in shares)			3,515,871															531,288	6,639,307
Issuance of stock	11,208			11,208													$ 29,186		$ 1	$ 29,185
Recognition of beneficial conversion feature	$ 0			2,762	(2,762)
Issuance of common stock for exercise of stock options (in shares)	5,411		5,411
Issuance of common stock for exercise of stock options	$ 14			14
Issuance of common stock for restricted share units vested (in shares)	74,804
Issuance of common stock for restricted share units vested	$ 0			0
Issuance of common stock under Employee Stock Purchase Plan (in shares)			280,139
Issuance of common stock under Employee Stock Purchase Plan	493			493
Stock-based compensation	4,090			4,090
Unrealized gain on marketable securities	0
Net loss	(72,111)				(72,111)
Issuance of Series X Convertible Preferred Stock in exchange for common stock (in shares)		(52,241)	522,410
Issuance of Series X Convertible Preferred Stock in exchange for common stock	0
Balance, ending (in shares) at Dec. 31, 2020		1,044,278	44,876,408
Balance, ending at Dec. 31, 2020	$ 10,715		$ 4	$ 345,411	$ (334,700)	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net loss	$ (72,111)	$ (41,092)	$ (59,016)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	286	328	523
Stock-based compensation	4,090	5,073	5,710
Non-cash interest expense	16	28	43
Amortization of discount or premium on short-term investments	0	0	31
Amortization of debt issuance costs	5	8	13
Operating lease right-of-use assets and liabilities, net	(57)	47	0
Deferred rent	0	0	30
Change in fair value of contingent forward purchase obligations	0	(411)	(3,851)
Contingent forward purchase obligation offering costs	0	0	211
Changes in operating assets and liabilities:
Accounts receivable	(11,165)	(10)	321
Prepaid expenses and other current assets	1,682	(2,936)	(532)
Accounts payable and accrued liabilities	6,591	(784)	(59)
Accrued compensation and benefits	1,045	1,244	822
Deferred revenue	15,207	9,803	0
Other assets	0	170	(951)
Net cash used in operating activities	(54,411)	(28,532)	(56,705)
Investing activities:
Purchases of short-term investments	0	0	(14,548)
Maturities of short-term investments	0	0	29,026
Purchases of property and equipment	(186)	(35)	(177)
Net cash (used in) provided by investing activities	(186)	(35)	14,301
Financing activities:
Proceeds from issuance of common stock	11,041	5,289	6,440
Proceeds from Registered Direct Offering, net of offering costs	0	0	49,509
Proceeds from exercise of stock options	14	7	204
Deferred public offering costs	0	(31)	0
Principal repayments of Term Loan	2,963	0	0
Net cash provided by financing activities	37,278	14,273	56,153
Net (decrease) increase in cash, cash equivalents, and restricted cash	(17,319)	(14,294)	13,749
Cash, cash equivalents, and restricted cash at beginning of year	60,268	74,562	60,813
Cash, cash equivalents, and restricted cash at end of year	42,949	60,268	74,562
Supplemental disclosure of cash flows:
Interest paid	445	616	582
Non-cash investing activity:
Purchases of property and equipment included in accounts payable and accrued liabilities	12	10	14
Non-cash financing activities:
Purchase of shares pursuant to Employee Stock Purchase Plan	493	411	570
Proceeds from public offering of common stock, net of issuance costs, included in prepaid expenses and other current assets	167	0	0
Vesting of early exercised stock options	0	0	21
Series X Convertible Preferred Stock
Financing activities:
Proceeds from issuance of common stock	29,186	0	0
Stock Purchase Agreement
Financing activities:
Proceeds from issuance of common stock	$ 0	$ 9,008	$ 0

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Basis of Presentation	THE COMPANY AND BASIS OF PRESENTATION Description of Business Cidara Therapeutics, Inc., or the Company, was originally incorporated in Delaware in December 2012 as K2 Therapeutics, Inc., and its name was changed to Cidara Therapeutics, Inc. in July 2014. The Company is a biotechnology company focused on the discovery, development and commercialization of long-acting therapeutics designed to transform the standard of care for patients facing serious fungal or viral infections. The Company’s lead product candidate is rezafungin acetate, an intravenous formulation of a novel echinocandin. Rezafungin is being developed as a once-weekly, high-exposure therapy for the first-line treatment and prevention of serious, invasive fungal infections. In addition, the Company is also using its Cloudbreak® antiviral platform to develop Antiviral Conjugates, or AVCs, for the prevention and treatment of influenza and other viral infections, including RSV, HIV and the SARS-CoV-2 strains causing COVID-19. The Company formed wholly-owned subsidiaries, Cidara Therapeutics UK Limited, in England, and Cidara Therapeutics (Ireland) Limited, in Ireland, in March 2016 and October 2018, respectively, for the purpose of developing its product candidates in Europe. Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2020, the Company had an accumulated deficit of $334.7 million. The Company expects to continue to incur net losses into the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. At December 31, 2020, the Company had cash, cash equivalents and restricted cash of $42.9 million. Based on the Company’s current business plan, management believes that existing cash and cash equivalents will not be sufficient to fund the Company’s obligations for twelve months from the issuance of these financial statements. The Company’s ability to execute its operating plan depends on its ability to obtain additional funding through equity offerings, debt financings or potential licensing and collaboration arrangements. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, the Company’s current working capital, anticipated operating expenses and net losses and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, raise substantial doubt about its ability to continue as a going concern for a period of one year following the date that these financial statements are issued. The consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through cash and cash equivalents on hand, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements. There can be no assurance that additional funds will be available when needed from any source or, if available, will be available on terms that are acceptable to the Company. Even if the Company raises additional capital, it may also be required to modify, delay or abandon some of its plans which could have a material adverse effect on the Company’s business, operating results and financial condition and the Company’s ability to achieve its intended business objectives. Any of these actions could materially harm the Company’s business, results of operations and future prospects. In addition to the foregoing, the Company is closely monitoring the impact of the COVID-19 pandemic on its business and has taken steps designed to protect the health and safety of its employees while continuing its operations. Given the level of uncertainty regarding the duration and impact of the COVID-19 pandemic on capital markets and the United States economy, the Company is currently unable to assess the impact of the COVID-19 pandemic on its future access to capital. The Company is continuing to monitor the spread of COVID-19 and its potential impact on the Company's operations. The full extent to which the COVID-19 pandemic will impact the Company's business, results of operations, financial condition, clinical trials, and preclinical research will depend on future developments that are highly uncertain, including actions taken to contain or treat COVID-19 and their effectiveness, as well as the economic impact on national and international markets. Basis of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. Reclassification of Prior Period Amounts Certain reclassifications have been made to prior period amounts to conform to the current-year presentation, including the reporting of accounts receivable as a separate line item on the Consolidated Balance Sheets as well as presenting changes in accounts receivable as a separate line item on the Consolidated Statements of Cash Flows. These reclassifications have no effect on the reported net loss for the years ended December 31, 2020, 2019 and 2018. Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s stock options, estimated collaboration expenses and incurred expenses related to the Mundipharma Collaboration Agreement, the fair value of the Company's contingent forward purchase obligations, and certain accruals, including those related to nonclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Cash, Cash Equivalents, and Restricted Cash The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents. Restricted cash represents cash that the Company is required to maintain on hand in order to maintain compliance with an operating covenant in the Third Amendment to the Company's Loan Agreement with Pacific Western Bank. See Note 5 for additional information. Accounts Receivable Accounts receivable are recorded at their net invoice value and are not interest bearing. We reserve specific receivables when collectibility is no longer probable. These reserves are re-evaluated on a regular basis and are adjusted, as needed. Once a receivable is deemed to be uncollectible, such balance is recorded as an allowance for credit losses. No such allowance existed at December 31, 2020 or 2019. Property and Equipment The Company records property and equipment at cost, which consists of lab equipment, computer equipment and software, office equipment, furniture and fixtures and leasehold improvements. Property and equipment is depreciated using the straight-line method over the estimated useful lives (generally three Concentration of Credit Risk The Company’s financial instruments that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in government insured financial institutions in excess of government insured limits. The Company invests its cash balances in financial institutions that it believes have high credit quality, has not experienced any losses on such accounts and does not believe it is exposed to significant credit risk. Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying statements of operations and comprehensive loss. Income Taxes The Company follows the Financial Accounting Standards Board, or FASB, Accounting Standards Codification , or ASC, 740, Income Taxes , or ASC 740, in reporting deferred income taxes. ASC 740 requires a company to recognize deferred tax assets and liabilities for expected future income tax consequences of events that have been recognized in the Company’s consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates in the years in which the temporary differences are expected to reverse. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions pursuant to ASC 740, which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured as the tax benefit having the highest likelihood of being realized upon ultimate settlement with the taxing authority. The Company recognizes interest accrued related to unrecognized tax benefits and penalties in the provision for income taxes. Revenue Recognition The Company recognizes revenue is accordance with ASC Topic 606, Revenue from Contracts with Customers , which applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. In a contract with multiple performance obligations, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation, which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price(s) may include estimates regarding forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. Any change made to estimated progress towards completion of a performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in a contract, the Company recognizes revenues from the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from the allocated transaction price. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue or expense recognition as a change in estimate. At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being reached. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or a collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of milestones that are within its or a collaboration partner’s control, such as operational developmental milestones and any related constraint, and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which will affect collaboration revenues and earnings in the period of adjustment. Revisions to the Company’s estimate of the transaction price may also result in negative collaboration revenues and earnings in the period of adjustment. For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, and a license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, the Company has not recognized any royalty revenue from collaborative arrangements. In September 2019, the Company entered into a Collaboration and License Agreement, or the Collaboration Agreement, with Mundipharma Medical Company, or Mundipharma. The Company concluded that there were three significant performance obligations under the Collaboration Agreement: the license, the research and development services, and the clinical supply services, and that the obligations are distinct from each other. Revenue associated with the license was recognized upon delivery in September 2019. The Company concluded that progress towards completion of the research and development and clinical supply performance obligations related to the Collaboration Agreement is best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The Company periodically reviews and updates the estimated collaboration expenses, when appropriate, which may adjust revenue recognized for the period. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in the period could be materially impacted. The transaction price to be recognized as revenue under the Collaboration Agreement consists of the upfront payment and estimated reimbursable research and development and clinical supply costs. Potential future payments for variable consideration, such as clinical, regulatory or commercial milestones, will be recognized when it is probable that, if recorded, a significant reversal will not take place. Potential future royalty payments will be recorded as revenue when the associated sales occur. See Note 8 for additional information. Research and Development Costs Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and nonclinical and clinical trial costs. The Company accrues nonclinical and clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies, and other events. Costs incurred in purchasing technology assets and intellectual property are charged to research and development expense if the technology has not been conclusively proven to be feasible and has no alternative future use. Grant Funding The Company has evaluated the terms of research and development grants to assess its obligations and the classification of funding received. Amounts billable for funded research and development are recognized in the statement of operations as a reduction to research and development expense over the grant period as the related costs are incurred to meet the Company's obligations. The Company recognized immaterial amounts as reductions to research and development expense due to funded grants for the years ended December 31, 2020, 2019 and 2018. Preclinical and Clinical Trial Accruals The Company makes estimates of its accrued expenses as of each balance sheet date in the financial statements based on the facts and circumstances known at that time. Accrued expenses for preclinical studies and clinical trials are based on estimates of costs incurred and fees that may be associated with services provided by contract research organizations, or CROs, clinical trial investigational sites and other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing for these services, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If possible, the Company obtains information regarding unbilled services directly from these service providers. However, the Company may be required to estimate these services based on other available information. If the Company underestimates or overestimates the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future periods. Historically, estimated accrued liabilities have approximated actual expense incurred. Subsequent changes in estimates may result in a material change in accruals. Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized gains on short-term investments. Comprehensive losses have been reflected in the consolidated statements of operations and comprehensive loss and as a separate component of the consolidated statements of convertible preferred stock and stockholders’ equity for all periods presented. Stock-based Compensation The Company accounts for stock-based compensation expense related to employee stock options, restricted stock and employee stock purchase plan rights by estimating the fair value on the date of grant. The Company estimates the fair value of stock option awards to employees and non-employees using the Black-Scholes option pricing model, which requires the input of highly subjective assumptions, including (a) the risk-free interest rate, (b) the expected volatility of our stock, (c) the expected term of the award, and (d) the expected dividend yield. Due to the lack of an adequate history of a public market for the trading of the Company's common stock and a lack of adequate company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. For these analyses, the Company has selected companies with comparable characteristics, including enterprise value, risk profiles, and position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company computes the historical volatility data using the daily close prices for the selected companies’ shares during the equivalent period of the calculated expected term of our stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its common stock price becomes available. The Company has estimated the expected life of its employee stock options using the “simplified” method, whereby the expected life equals the average of the vesting term and the original contractual term of the option. The risk-free interest rates for periods within the expected life of the option are based on the yields of zero-coupon U.S. treasury securities. The fair value of Restricted Stock Units, or RSUs, and Performance-based RSUs, or PRSUs, granted to employees is estimated based on the closing price of the Company's common stock on the date of grant. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. For awards subject to performance-based vesting conditions, the Company assesses the probability of achievement of the individual milestones under the stock-based awards and recognizes stock-based compensation expense over the implicit service period commencing once the Company believes the performance criteria is probable of achievement. The Company accounts for stock options, RSUs, and PRSUs granted to non-employees using the fair value approach. These stock-based awards are subject to periodic revaluation over their vesting terms. The Company recognizes forfeitures related to stock-based compensation as they occur. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss allocable to common shares by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss allocable to common shares by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of warrants, Series X Convertible Preferred Stock, as well as RSUs, PRSUs and options outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding. Net loss allocable to common shares for the years ended December 31, 2020 and 2018 includes non-cash deemed dividends of $2.8 million and $10.3 million, respectively, resulting from the recognition of beneficial conversion features. See Note 6 for additional information. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because doing so would be anti-dilutive (in common stock equivalent shares): December 31, 2020 2019 2018 Common stock warrants 12,517,328 12,517,328 12,517,328 Series X Convertible Preferred stock 10,442,780 5,652,310 4,452,310 Common stock options, RSUs and PRSUs issued and outstanding 6,787,033 5,360,563 4,392,671 Total 29,747,141 23,530,201 21,362,309 Fair Value of Financial Instruments The Company follows ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, restricted cash, accounts receivable, accounts payable, accrued liabilities, and a term loan. Fair value estimates of these instruments are made at each reporting period end based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, restricted cash, accounts receivable, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The Company believes that the fair value of long-term debt approximates its carrying value. Recently Issued Accounting Standards Recently Issued Accounting Standards Not Yet Adopted In December 2019, the FASB issued ASU 2019-12, "Simplifying the Accounting for Income Taxes," which eliminates certain exceptions within ASC 740, Income Taxes, and clarifies other aspects of the current guidance to promote consistency among reporting entities. The updated guidance is effective for interim and annual periods beginning after December 15, 2020. Early adoption is permitted. The Company does not expect the standard to have a material impact on its financial statements upon adoption. In August 2020, the FASB issued ASU 2020-06, "Accounting for Convertible Instruments and Contracts in an Entity's Own Equity," simplifies the accounting for certain convertible instruments by removing the separation models for convertible debt with a cash conversion feature or convertible instruments with a beneficial conversion feature. Additionally, this ASU amends the diluted EPS calculation for convertible instruments by requiring the use of the if-converted method. The treasury stock method is no longer available. Entities may adopt this ASU using either a full or modified retrospective approach, and it is effective for interim and annual reporting periods beginning after December 15, 2021. Early adoption is permitted for interim and annual reporting periods beginning after December 15, 2020. The Company is assessing the impact the adoption of this ASU will have on its financial statements. Recently Adopted Accounting Standards In August 2018, the FASB issued ASU 2018-13, "Changes to the Disclosure Requirements for Fair Value Measurement," which modifies certain disclosure requirements on fair value measurements. The Company adopted ASU 2018-13 effective January 1, 2020. The adoption of this standard did not have a material impact on the Company's financial statements. In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." The updated guidance replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 requires that an entity measure and recognize expected credit losses for financial assets held at amortized cost and replaces the incurred loss impairment methodology in prior GAAP with a methodology that requires consideration of a broader range of information to estimate credit losses, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The Company follows ASC 820-10, Fair Value Measurements and Disclosures , which among other things, defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. Based on the borrowing rates available to the Company for loans with similar terms, which is considered a Level 2 input as described below, the Company believes that the fair value of long-term debt approximates its carrying value. As a basis for considering such assumptions, a three-tier fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs for which there is little or no market data, which require the reporting entity to develop its own assumptions, which reflect those that a market participant would use. The Company classifies investments in money market funds within Level 1 as the prices are available from quoted prices in active markets. Investments in commercial paper, corporate debt and reverse repurchase agreements are classified within Level 2 as these instruments are valued using observable market inputs including reported trades, broker/dealer quotes, bids and/or offers. As discussed in Note 6, on May 21, 2018, the Company entered into a subscription agreement with certain investors providing for the purchase and sale of up to an aggregate of $120.0 million of its common stock and preferred stock in three closings. The second and optional third closings and warrants related to the optional third closing, which were to be triggered by the Company's announcement of topline data of Part B of its STRIVE Phase 2 clinical trial of rezafungin, contained features for subsequent closings that were not solely within the control of the Company and that embodied an obligation that the Company would have settled by issuing a variable number of shares when the obligation was based predominantly on having a fixed value at inception. In accordance with ASC 480, "Distinguishing Liabilities from Equity," the Company determined that these closings were classified as liabilities and represented contingent forward purchase obligations. These liabilities were required to be recorded at their estimated fair value initially and on a recurring basis. The contingent forward purchase obligations were classified within Level 3 of the fair value hierarchy as the Company was using a probability-weighted valuation approach, utilizing significant unobservable inputs including the probability and estimated timing of achieving positive or negative results associated with Part B of the STRIVE Phase 2 clinical trial and estimated discount rates related to the risk of achievement of the expected equity issuances. The liability was initially recorded at $4.3 million on May 21, 2018. Fair value adjustments resulting in gains of $0.4 million and $3.9 million were recorded during the years ended December 31, 2019 and 2018, respectively. The contingent forward purchase obligation did not exist as of December 31, 2020 and December 31, 2019. None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. The following tables summarize the Company’s financial instruments measured at fair value on a recurring basis (in thousands): TOTAL LEVEL 1 LEVEL 2 LEVEL 3 December 31, 2020 Assets: Cash and money market accounts $ 35,912 $ 35,912 $ — $ — Restricted cash and money market accounts 7,037 7,037 — — Total assets at fair value $ 42,949 $ 42,949 $ — $ — December 31, 2019 Assets: Cash and money market accounts $ 50,268 $ 50,268 $ — $ — Restricted cash and money market accounts 10,000 10,000 — — Total assets at fair value $ 60,268 $ 60,268 $ — $ —

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT Property and equipment consists of the following (in thousands): December 31, 2020 2019 Laboratory equipment $ 2,304 $ 2,104 Leasehold improvements 425 425 Computer hardware and software 404 481 Office equipment 119 119 Furniture and fixtures 142 142 3,394 3,271 Less accumulated depreciation and amortization (3,052) (2,842) Total $ 342 $ 429 Depreciation and amortization of property and equipment of $0.3 million, $0.3 million and $0.5 million were recorded for the years ended December 31, 2020, 2019 and 2018, respectively.

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	DEBT On October 3, 2016, the Company entered into a loan and security agreement, or the Loan Agreement, with Pacific Western Bank, as the collateral agent and a lender, or Lender, pursuant to which the Lender agreed to lend to the Company up to $20.0 million in a series of term loans. Contemporaneously, the Company borrowed $10.0 million from the Lender, or Term A Loan. Under the terms of the Loan Agreement, because the Company achieved positive clinical results from the STRIVE Phase 2 clinical trial of rezafungin by March 31, 2018, or the Milestone, the Company had the option to borrow, at its sole discretion, until October 3, 2018, from the Lender up to an additional $10.0 million, or Term B Loan. The Company did not borrow any funds available under the Term B Loan before the draw period ended. The Company’s obligations under the Loan Agreement are secured by a first priority security interest in substantially all of the Company’s current and future assets, other than its intellectual property, which is subject to a double negative pledge. The Company may prepay the borrowed amounts, provided that the Company will be obligated to pay a prepayment fee equal to (i) 2.0% of the applicable principal amount of the Term Loan if the prepayment occurs before the first anniversary of the applicable funding date, and (ii) 1.0% of the applicable principal amount of the Term Loan if the prepayment occurs after the first anniversary of the funding date of such Term Loan but on or prior to the second anniversary of the funding date of such Term Loan. While any amounts are outstanding under the Loan Agreement, the Company is subject to a number of affirmative and restrictive covenants, including covenants regarding dispositions of property, business combinations or acquisitions, incurring additional indebtedness and transactions with affiliates, among other customary covenants. The Company is also restricted from paying dividends or making other distributions or payments on its capital stock, subject to limited exceptions. Pursuant to the Loan Agreement, on October 3, 2016, the Company issued to the Lender a warrant to purchase an aggregate of up to 17,331 shares of the Company’s common stock at an exercise price of $11.54 per share. If the Company borrows additional amounts under the Loan Agreement, it will, in connection with any such borrowing, issue the Lender an additional warrant to purchase that number of shares of the Company’s common stock as is equal to 2.0% of the additional principal amount borrowed divided by the exercise price. The exercise price shall be equal to the 30-day average closing price of the Company’s common stock, calculated as of the date immediately prior to the date of such additional borrowing. The warrants are immediately exercisable and will expire ten years from the date of the grant. On June 13, 2018, the Company and the Lender entered into a First Amendment to the Loan Agreement, which reset the Milestone to require the Company to achieve positive data from Part B of the STRIVE Phase 2 clinical trial of rezafungin on or prior to July 31, 2019. On July 27, 2018, the Company and the Lender entered into a Second Amendment to the Loan Agreement, which amended, among other things, the interest-only period, the date of maturity, or Maturity Date, and the interest rate. The interest-only period will be followed by equal monthly payments of principal and interest. The Term Loans will bear interest at a variable annual rate equal to the greater of (i) 4.5% or (ii) the Lender’s prime interest rate plus 0.75%. At December 31, 2020, the Term Loans bear interest at 4.50%. On July 29, 2019, the Company announced positive data from Part B of the STRIVE clinical trial, which satisfied the Milestone. Within 30 days of satisfying the Milestone, the Company was required to agree with the Lender on an amendment to the Loan Agreement to define a new financial covenant and/or milestone for fiscal year 2019 and all subsequent fiscal years during the term of the Loan Agreement. On August 27, 2019, the Lender extended the deadline to execute this amendment to October 15, 2019, and on October 11, 2019, the Lender further extended this deadline until November 7, 2019. On November 5, 2019, the Company and the Lender entered into a Third Amendment to the Loan Agreement, which reset the operating covenant to require the Company to maintain cash equal to or greater than the Company's outstanding indebtedness to the Lender, which is equivalent to a compensating balance and results in a restricted cash balance of $7.0 million and $10.0 million as of December 31, 2020 and 2019, respectively. The amendment also extended the interest-only period through April 3, 2020 and the maturity date through July 3, 2022. The Company evaluated the First, Second and Third Amendments and determined that the amendments did not represent a substantial change from the original Loan Agreement. Accordingly, the Company accounted for the amendments as debt modifications. Costs previously deferred under the original terms of the Loan Agreement are amortized into interest expense over the new term of the Third Amendment. Upon the occurrence of certain events, including but not limited to the Company’s failure to satisfy its payment obligations under the Loan Agreement, the breach of certain of its other covenants under the Loan Agreement, or the occurrence of a material adverse change, the Lender has the right, among other remedies, to declare all principal and interest and other amounts due to the Lender under the Loan Agreement immediately due and payable. The principal payments due under the Loan Agreement have been classified as a current liability at December 31, 2020 and 2019 due to the considerations discussed in Note 1 and the assessment that the material adverse change clause under the Loan Agreement is not within the Company's control. The Company has not been notified of an event of default by the Lenders as of the date of the filing of this Form 10-K. As of December 31, 2020, future principal payments due under the Third Amendment of the Term A Loan are as follows (in thousands): Year ended: December 31, 2021 $ 4,444 December 31, 2022 2,593 Total future principal payments due under the Term A Loan $ 7,037 The fair value of the warrants to purchase common stock issued in connection with Term Loan A was estimated on the date of issuance using the Black-Scholes valuation model and recorded to additional paid-in capital. The fair value of the warrants on the date of issuance as well as the debt issuance costs incurred in connection with the entry into the Loan Agreement are presented as a direct deduction from the carrying amount of the term loan on the consolidated balance sheet and are being amortized utilizing the effective interest method over the term of the loan. The Company recorded interest expense of $21,000, $36,000 and $56,000 for the years ended December 31, 2020, 2019 and 2018, respectively, for the amortization of the fair value of the warrants and debt issuance costs.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS’ EQUITY 2020 Rights Offering On January 22, 2020, the Company initiated a rights offering to raise gross proceeds of $30.0 million through the distribution of subscription rights to holders of its common stock, Series X Preferred Stock, and warrants to purchase common stock issued on May 21, 2018, or the Rights Offering. On February 12, 2020, the Company sold 6,639,307 shares of common stock and 531,288 shares of Series X Preferred Stock for $2.51 and $25.10 per share, respectively, for aggregate gross proceeds of $30.0 million. Total offering costs of $0.8 million were offset against the proceeds from the sale of common stock for total net proceeds of $29.2 million. The Rights Offering was fully backstopped by Biotechnology Value Fund, L.P., or BVF, and Stonepine Capital, LP, or Stonepine. With respect to the Series X Convertible Preferred Stock, because the effective conversion price on the commitment date was below the fair value of the common stock at the date of issuance, a beneficial conversion feature with a calculated fair value of $2.8 million existed at the issuance date. As the Series X Convertible Preferred Stock is fully convertible at issuance, the full $2.8 million was recorded at issuance as a deemed dividend on February 12, 2020. This non-cash deemed dividend impacted accumulated deficit and additional paid in capital at December 31, 2020 and net loss attributable to common stockholders and net loss attributable to common stockholders per share for the year ended December 31, 2020. With respect to the common stock, because the purchase price was below fair value on the issuance date, a bonus element exists at the issuance date. Basic and diluted net loss per common share and shares used to compute basic and diluted net loss per common share have been retroactively adjusted for all periods presented to reflect this bonus element. Mundipharma Stock Purchase Agreement — On September 3, 2019, the Company entered into a Stock Purchase Agreement, with Mundipharma AG, or the Purchaser, a related party, pursuant to which the Company issued to the Purchaser 4,781,408 shares of its common stock, or the Shares, in a private placement at a price per share of $1.884 (a 20% premium to the volume weighted average price of the Company’s common stock for the 10 trading days prior to September 3, 2019) for an aggregate purchase price of approximately $9.0 million. May 2018 Registered Direct Offering — On May 21, 2018, the Company entered into a subscription agreement with certain investors providing for the purchase and sale, in a registered direct offering, of up to an aggregate of $120.0 million of its common stock and preferred stock in three closings. On May 23, 2018, the Company completed the first closing, which was comprised of 6,185,987 shares of common stock at an offering price of $4.70 per share, 445,231 shares of Series X Convertible Preferred Stock at an offering price of $47.00 per share, and an option fee relating to the third closing paid by the investors for a total of $0.5 million. In a private placement concurrent with the first closing, or the First Private Placement, the Company also sold warrants, at $0.125 per warrant share, to purchase an aggregate of 12,499,997 shares of common stock. Net proceeds for the first closing and the First Private Placement were $49.5 million. The Company performed an analysis to allocate the proceeds from the May 2018 registered direct offering to the offering's various components on a relative fair value basis, including the contingent forward purchase obligations (discussed further in Note 4) as well as the common stock, Series X Convertible Preferred Stock, warrants, and option fee. With respect to the Series X Convertible Preferred Stock, because the adjusted conversion price on the commitment date (following the allocation of proceeds on a fair value basis) was below the fair value of the common stock at the date of issuance, a beneficial conversion feature with a calculated fair value of $10.3 million existed at the issuance date. The beneficial conversion feature is amortized as a deemed dividend to the preferred holders. As the Series X Convertible Preferred Stock is fully convertible at issuance, the full amortization of the $10.3 million was recorded at issuance as a deemed dividend on May 23, 2018. This non-cash deemed dividend impacted net loss attributable to common stockholders and net loss attributable to common stockholders per share for the year ended December 31, 2018. The second closing of the registered direct offering was contingent on the Company's announcement of topline data from Part B of its STRIVE global randomized Phase 2 clinical trial of rezafungin provided that the Company would not be obligated to complete the second closing if the purchase price was less than $4.70 per share, and the third closing of the registered direct offering was to occur after the second closing, but at the Company's option. On July 29, 2019, the Company announced positive data from Part B of its STRIVE clinical trial. Because the volume weighted average price of the Company's common stock for the five trading days following the public release of topline data from Part B of the STRIVE clinical trial of rezafungin was below $6.81, the resulting purchase price for the second and third closings of the May 2018 registered direct offering would have been less than $4.70 per share. Accordingly, the Company was unable to complete the second and third closings without first obtaining the approval of its stockholders. On August 7, 2019, the Company notified the purchasers in the May 2018 registered direct offering that it had elected not to consummate the second closing of the offering. Accordingly, the obligations of the parties to the registered direct offering terminated and are of no further force or effect, and the second closing will not be held. As a result of this election, the optional third closing of the offering and the related concurrent private placement of warrants will not be held. Preferred Stock — Under the amended and restated certificate of incorporation, the Company’s board of directors has the authority, without further action by the stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding. The Company had 10,000,000 shares of preferred stock authorized at December 31, 2020. In May 2018, the Company designated 5,000,000 shares of preferred stock as Series X Convertible Preferred Stock with a par value of $0.0001 per share. On March 22, 2019, the Company entered into an Exchange Agreement with Biotechnology Value Fund, L.P., and certain of its affiliated entities (collectively, BVF), pursuant to which BVF, without monetary consideration, agreed to exchange an aggregate of 1,200,000 shares of the Company’s common stock for an aggregate of 120,000 shares of the Company’s Series X Convertible Preferred Stock. On August 12, 2020, at the request of certain holders, 52,241 shares of the Company’s Series X Convertible Preferred Stock were converted to an aggregate of 522,410 shares of the Company’s common stock. The specific terms of the Series X Convertible Preferred Stock are as follows: Conversion: Each share of Series X Convertible Preferred Stock is convertible at the option of the holder into 10 shares of common stock. Holders are not permitted to convert Series X Convertible Preferred Stock into common stock if, after conversion, the holder, its affiliates, and any other person whose beneficial ownership of common stock would be aggregated with the holder's for purposes of Section 13(d) or Section 16 of the Exchange Act, would beneficially own more than 9.99% of the number of shares of common stock outstanding immediately after the conversion. Dividends: Holders of Series X Convertible Preferred Stock are not entitled to receive any dividends except to the extent that dividends are paid on the Company's common stock. If dividends are paid on shares of common stock, holders of Series X Convertible Preferred Stock are entitled to participate in such dividends on an as-converted basis. Liquidation: Upon the liquidation, dissolution, or winding up of the company, each holder of Series X Convertible Preferred Stock will participate pari passu with any distribution of proceeds to holders of common stock. Voting: Shares of Series X Convertible Preferred Stock will generally have no voting rights, except as required by law and except that the consent of the holders of a majority of the outstanding Series X Convertible Preferred Stock will be required to amend the terms of the Series X Convertible Preferred Stock , if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series X Convertible Preferred Stock, or to increase or decrease (other than by conversion) the number of authorized shares of Series X Convertible Preferred Stock. The Company evaluated the Series X Convertible Preferred Stock for liability or equity classification under ASC 480, Distinguishing Liabilities from Equity , and determined that equity treatment was appropriate because the Series X Convertible Preferred Stock did not meet the definition of liability instruments defined thereunder as convertible instruments. Additionally, the Series X Convertible Preferred Stock is not redeemable for cash or other assets (i) on a fixed or determinable date, (ii) at the option of the holder, and (iii) upon the occurrence of an event that is not solely within control of the Company. Common Stock —The Company had 200,000,000 shares of common stock authorized as of December 31, 2020. Holders of outstanding shares of common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the holders of common stock. Subject to the rights of the holders of any class of the Company’s capital stock having any preference or priority over common stock, the holders of common stock are entitled to receive dividends that are declared by the Company’s board of directors out of legally available funds. In the event of a liquidation, dissolution or winding-up, the holders of common stock are entitled to share ratably in the net assets remaining after payment of liabilities, subject to prior rights of preferred stock, if any, then outstanding. The common stock has no preemptive rights, conversion rights, redemption rights or sinking fund provisions, and there are no dividends in arrears or default. All shares of common stock have equal distribution, liquidation and voting rights, and have no preferences or exchange rights. In November 2017 the Company began to sell shares of common stock under a controlled equity offering sales agreement with Cantor Fitzgerald & Co. During the year ended December 31, 2018, the Company sold 847,937 shares of common stock for net proceeds of approximately $6.4 million after deducting placement agent fees. In September 2019, the Company began to sell shares of common stock under a controlled equity offering sales agreement with Cantor Fitzgerald & Co. During the years ended December 31, 2020 and 2019, the company sold 3,515,871 and 2,095,887 shares of common stock for net proceeds of approximately $11.2 million and $5.3 million, respectively, after deducting placement agent fees. Common Stock Warrants As of December 31, 2020 and 2019, warrants to purchase 12,517,328 shares of the Company's common stock were outstanding with a weighted average exercise price of $6.82 per share. The warrants had no intrinsic value at December 31, 2020 and 2019. The intrinsic value of a common stock warrant is the difference between the market price of the common stock at the measurement date and the exercise price of the warrant. Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows (in common stock equivalent shares): December 31, 2020 2019 Common stock warrants 12,517,328 12,517,328 Series X Convertible Preferred stock 10,442,780 5,652,310 Stock options, RSUs and PRSUs issued and outstanding 6,787,033 5,360,563 Authorized for future stock awards 2,813,131 559,898 Awards available under the ESPP 521,986 463,741 Total 33,082,258 24,553,840

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Equity Incentive Plans	EQUITY INCENTIVE PLANS 2020 Inducement Incentive Plan and 2015 Equity Incentive Plan In December 2020, the Company's board of directors approved and adopted the 2020 Inducement Incentive Plan, or 2020 IIP. Under the 2020 IIP, the Company may grant stock options, stock appreciation rights, restricted stock, RSUs, and other awards to individuals who were not previously employees or directors of the Company, or who are returning to employment following a bona fide period of non-employment with the Company, as an inducement material to such persons entering into employment with the Company. In March 2015, the Company’s board of directors and stockholders approved and adopted the 2015 Equity Incentive Plan, or 2015 EIP. Under the 2015 EIP, the Company may grant stock options, stock appreciation rights, restricted stock, RSUs, and other awards to individuals who are employees, officers, directors or consultants of the Company. The number of shares of stock available for issuance under the 2015 EIP is automatically increased each January 1 by 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number as determined by the Company’s board of directors. Terms of stock award agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the 2020 IIP and 2015 EIP. Stock options granted by the Company generally vest over a three four 2015 Employee Stock Purchase Plan In March 2015, the Company’s board of directors and stockholders approved and adopted the 2015 Employee Stock Purchase Plan, or ESPP. The number of shares of stock available for issuance under the ESPP is automatically increased each January 1 by the lesser of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 490,336 shares, or (iii) such lesser number as determined by the Company’s board of directors. The ESPP allows substantially all employees to purchase the Company’s common stock through a payroll deduction at a price equal to 85% of the lower of the fair market value of the stock as of the beginning or the end of each purchase period. An employee’s payroll deductions under the ESPP are limited to 15% of the employee’s eligible compensation. During the years ended December 31, 2020, 2019 and 2018, 280,139, 242,501 and 158,066 shares, respectively, were issued pursuant to the ESPP. Restricted Stock Units The following table summarizes RSU and PRSU activity during the year ended December 31, 2020: Number of Weighted Average Grant Date Fair Value Outstanding at December 31, 2019 383,885 $ 3.97 RSUs and PRSUs granted 151,475 2.29 RSUs and PRSUs vested (74,804) 4.18 RSUs and PRSUs canceled (32,321) 5.40 Outstanding at December 31, 2020 428,235 $ 3.55 The weighted-average grant date fair value of RSUs and PRSUs granted during the years ended December 31, 2019 and 2018 was $2.88 and $3.83, respectively, per share. The total fair value of RSUs and PRSUs vested during the years ended December 31, 2020 and 2019 was approximately $0.3 million and $0.5 million, respectively, and was immaterial for the year ended December 31, 2018. At December 31, 2020, estimated unrecognized compensation expense related to RSUs and PRSUs granted was approximately $1.3 million. 2019 Option Exchange On November 20, 2019, the Company commenced an option exchange program pursuant to which it offered to certain employees the option to exchange some or all of their outstanding stock options, whether vested or unvested, for new stock options, or the Option Exchange. Stock options were eligible for exchange, or Eligible Options, if they had an exercise price greater than the greater of (i) $2.28 and (ii) the closing price of the Company's common stock on December 18, 2019, or the Exchange Date. An exchange ratio of 1 for 1 was applied to options held by eligible employees who were not executive officers for purposes of Section 16 of the Exchange Act as designated by the Board, or a Section 16 Officer, and an exchange ratio of 1.5 for 1 applied to options held by Section 16 officers. The Option Exchange closed on December 18, 2019. Eligible Options to purchase an aggregate of 1,656,379 shares of the Company's common stock, representing 60.4% of the total shares underlying the Eligible Options were exchanged for new options to purchase 1,529,814 of the Company's common stock at $2.45 per share, the closing price of the Company's common stock on the Exchange Date. All surrendered options were canceled effective as of the closing of the Option Exchange. These new options were granted pursuant to the 2015 EIP and vest over one Stock Options The following table summarizes stock option activity during the year ended December 31, 2020: Number of Weighted Weighted Total Aggregate Outstanding at December 31, 2019 4,976,678 $ 4.37 7.27 $ 3,880 Options granted 1,747,000 2.15 Options exercised (5,411) 2.55 Options canceled (359,469) 7.30 Outstanding at December 31, 2020 6,358,798 $ 3.59 7.04 $ 55 Vested and expected to vest at December 31, 2020 6,358,798 $ 3.59 7.04 $ 55 Exercisable at December 31, 2020 4,160,074 $ 4.21 6.26 $ 31 The intrinsic value of a stock option is the difference between the market price of the common stock at the measurement date and the exercise price of the option. The following table summarizes the Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted to employees under our equity incentive plans and the shares purchasable under our 2015 ESPP during the periods presented: For the years ended December 31, 2020 2019 2015 EIP and 2020 IIP Risk-free interest rate 0.30% - 1.66% 1.42% - 2.57% Expected dividend yield 0% 0% Expected volatility 82% - 85% 80% - 82% Expected term (years) 5.27 - 6.08 5.27 - 6.08 2015 ESPP Risk-free interest rate 0.08% - 0.17% 1.55% - 2.42% Expected dividend yield 0% 0% Expected volatility 65% - 105% 67% - 82% Expected term (years) 0.50 - 2.00 0.50 - 2.00 Stock-based compensation expense recognized for restricted shares, RSUs, PRSUs, stock options, and the ESPP has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years ended December 31, 2020 2019 2018 Research and development $ 2,089 $ 2,502 $ 2,676 General and administrative 2,001 2,571 3,034 Total $ 4,090 $ 5,073 $ 5,710 The weighted-average grant date fair value of stock options granted during the years ended December 31, 2020, 2019 and 2018 was $1.48, $1.78 and $2.98, respectively, per share. The total intrinsic value of stock options exercised during the years ended December 31, 2020 and 2019 was immaterial, and approximately $0.2 million during the year ended December 31, 2018. As of December 31, 2020, total unrecognized share-based compensation expense related to unvested stock options was approximately $3.4 million. This unrecognized compensation cost is expected to be recognized over a weighted-average period of approximately 1.89 years. As of December 31, 2020, total unrecognized compensation expense related to the Company’s ESPP was approximately $0.1 million. This unrecognized compensation cost is expected to be recognized over approximately 0.57 years.

Significant Agreements and Cont

Significant Agreements and Contracts	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant Agreements and Contracts	SIGNIFICANT AGREEMENTS AND CONTRACTS Mundipharma Collaboration Agreement On September 3, 2019, the Company entered into a Collaboration and License Agreement, or the Collaboration Agreement, with Mundipharma, a related party, for a strategic collaboration to develop and commercialize rezafungin in an intravenous formulation, or the Licensed Product for the treatment and prevention of invasive fungal infections. Under the Collaboration Agreement, the Company is responsible for leading the conduct of an agreed global development plan, or the Global Development Plan, that includes the Company’s ongoing Phase 3 pivotal clinical trial of the Licensed Product for the treatment of candidemia and/or invasive candidiasis, or the ReSTORE Trial, and the Company’s planned Phase 3 pivotal clinical trial of the Licensed Product for the prophylaxis of invasive fungal infections in adult allogeneic blood and marrow transplant recipients, or the ReSPECT Trial, as well as specified GLP-compliant non‑clinical studies and chemistry, manufacturing and controls, or CMC, development activities for the Licensed Product. Mundipharma is responsible for performing all development activities, other than Global Development Plan activities, that may be necessary to obtain and maintain regulatory approvals for the Licensed Product in the Mundipharma Territory, at Mundipharma’s sole cost. Pursuant to the Collaboration Agreement, the Company granted Mundipharma an exclusive, royalty‑bearing license to develop, register and commercialize the Licensed Product outside of the United States and Japan, or the Mundipharma Territory, subject to the Company’s retained right to lead a global development program for the Licensed Product in both the Mundipharma Territory and in the United States and Japan, or the Company Territory, as described below. The Company also granted Mundipharma an option to obtain exclusive licenses to develop, register and commercialize rezafungin in a formulation for subcutaneous administration, or Subcutaneous Product, and in formulations for other modes of administration, or Other Products, in the Mundipharma Territory, subject to similar retained rights of the Company to conduct mutually agreed global development activities for such products. In addition, the Company granted Mundipharma a co‑exclusive, worldwide license to manufacture the Licensed Product and rezafungin. Until the seventh anniversary of the first commercial sale of the Licensed Product in the Mundipharma Territory, each party has granted the other party an exclusive, time-limited right of first negotiation to obtain a license to any anti-fungal product (other than Licensed Product, Subcutaneous Product and Other Products) that such party proposes to out-license in the other party’s territory. However, in the event of the acquisition of a party by a third party, this right of first negotiation will not apply to any such anti‑fungal product of the acquiring third party prior to consummation of the acquisition of such party, acquired by such acquiring third party from another third party after consummation of the acquisition of such party, or developed internally by the acquiring third party, either before or after consummation of the acquisition of such party, without the use of, reliance upon or reference to any technology of the acquired party that is licensed to the other party under the Collaboration Agreement, any technology of the other party that is licensed to the acquired party under the Collaboration Agreement, or any technology jointly developed by the parties pursuant to the Collaboration Agreement. The Company retains the exclusive right to develop, register and commercialize the Licensed Product, Subcutaneous Product and Other Products in the Company Territory, and Mundipharma has granted the Company certain licenses under Mundipharma-controlled technology and jointly-developed technology to develop, register and commercialize Licensed Product, Subcutaneous Product and Other Products in the Company Territory and to manufacture such products and rezafungin worldwide. The parties have agreed to share equally (50/50) the costs of Global Development Plan activities, or Global Development Costs, subject to a cap on Mundipharma’s Global Development Cost share of $31.2 million. The Company would receive additional financial support for Global Development Plan activities through a near-term milestone payment by Mundipharma of $11.1 million. Mundipharma is entitled to credit the full amount of this milestone payment toward future royalties payable to the Company, subject to a limit on the amount by which royalty payments to the Company may be reduced in any quarter. If Mundipharma has not fully credited the amount of such milestone payment toward royalties payable to the Company before the earlier of (i) December 31, 2024 and (ii) termination of the Collaboration Agreement by Mundipharma, the Company will be obligated to refund the uncredited portion of such milestone payment to Mundipharma on the earlier of such dates. The total potential transaction value is $568 million, including an equity investment (see Note 6 for additional information), an up-front payment, global development funding, and certain development, regulatory, and commercial milestones. The Company is also eligible for double-digit royalties in the teens on tiers of annual net sales. Either party may terminate the Collaboration Agreement for uncured material breach by the other party. Mundipharma may terminate the Collaboration Agreement at will, provided that if Mundipharma terminates the Collaboration Agreement in its entirety prior to the last visit of the last patient in both the ReSPECT Trial and the ReSTORE Trial, Mundipharma will continue to be liable for its share of Global Development Costs as described above. The Company may terminate the Agreement if Mundipharma or any of its affiliates or sublicensees, directly or indirectly through any third party, commences any interference or opposition proceeding with respect to, challenges the validity or enforceability of, or opposes any extension of or the grant of a supplementary protection certificate with respect to, any of the Company's patent rights licensed to Mundipharma, or upon an insolvency event of Mundipharma. Revenue Recognition The Company determined the transaction price is equal to the up-front fee of $30 million plus the research and development funding of $31.2 million. The common stock issued pursuant to the Mundipharma Stock Purchase Agreement was determined to be issued at fair market value after applying a lack of marketability discount as Mundipharma received restricted shares. Therefore, no additional premium or discount was allocated to the transaction price of the Agreement for the share issuance. The transaction price was allocated to the performance obligations on the basis of the relative stand-alone selling price estimated for each performance obligation. In estimating the stand-alone selling price for each performance obligation, the Company developed assumptions that require judgment and included forecasted revenues, expected development timelines, discount rates, probabilities of technical and regulatory success and costs for manufacturing clinical supplies. A description of the distinct performance obligations identified under the Agreement, as well as the amount of revenue allocated to each distinct significant performance obligation, is as follows: Licenses of Intellectual Property. The license to the Company’s intellectual property, bundled with the associated know-how, represents a distinct performance obligation. The license and associated know-how was transferred to Mundipharma during September 2019, therefore the Company recognized the full revenue related to this performance obligation in the amount of $17.9 million in September 2019 as collaboration revenue in its condensed consolidated statements of operations and comprehensive loss. Research and Development Services. The Company and Mundipharma share equally in the costs of ongoing rezafungin clinical development in the Licensed Territory up to the specified cap, which represents a distinct performance obligation. The Company records these cost-sharing payments due from Mundipharma as collaboration revenue. The Company concluded that progress towards completion of the performance obligation related to the research and development services is best measured in an amount proportional to the research and development expenses incurred and the total estimated research and development expenses. Clinical Supply Services. The Company's initial obligation to supply rezafungin for ongoing clinical development in the Licensed Territory represents a distinct performance obligation. The Company concluded that progress towards completion of the performance obligations related to the clinical supply services is best measured in an amount proportional to the clinical supply services expenses incurred and the total estimated clinical supply services. Milestone Payments. The Company determined that as of December 31, 2020, all the potential milestone payments are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company's control or are otherwise constrained under the variable consideration guidance. Therefore, these payments have been fully constrained and are therefore not included in the transaction price. At the end of each subsequent reporting period, the Company will re-evaluate the probability of achievement of each milestone and any related constraint. In November 2020, the Company achieved a $11.1 million milestone under the Agreement, which is recorded as long-term deferred revenue as of December 31, 2020 because the rights to consideration is not expected to be satisfied within one year. The Company received payment for this milestone in January 2021. Mundipharma is entitled to credit the full amount of this milestone payment toward future royalties payable to the Company, subject to a limit on the amount by which royalty payments to the Company may be reduced in any quarter. If Mundipharma has not fully credited the amount of such milestone payment toward royalties payable to the Company before the earlier of (i) December 31, 2024 and (ii) termination of the Mundipharma Collaboration Agreement by Mundipharma, the Company will be obligated to refund the uncredited portion of such milestone payment to Mundipharma on the earlier of such dates. No revenue related to milestones was recognized during the years ended December 31, 2020, 2019 and 2018. Royalties. As the license is deemed to be the predominant item to which sales-based royalties relate, the Company will recognize revenue when the related sales occur. No royalty revenue was recognized during the years ended December 31, 2020, 2019 and 2018. The following table presents a summary of the activity in the Company's contract liabilities (recorded as deferred revenue on the balance sheet) during the year ended December 31, 2020 (in thousands): Opening balance, December 31, 2019 $ 9,803 Payments received 16,129 Milestone payment receivable 11,145 Revenue from performance obligations satisfied during reporting period (12,067) Closing balance, December 31, 2020 $ 25,010 Current portion of deferred revenue $ 13,865 Long-term portion of deferred revenue 11,145 Total deferred revenue, December 31, 2020 $ 25,010 The following table presents our contract revenues disaggregated by timing of revenue recognition (in thousands): Years Ended December 31 2020 2019 Point in Time Over Time Point in Time Over Time Revenue from Mundipharma Collaboration Agreement: License of Intellectual Property $ — $ — $ 17,861 $ — Research and Development Services — 10,513 — 2,670 Clinical Supply Services — 1,554 — 384 Total revenue from Mundipharma Collaboration Agreement $ — $ 12,067 $ 17,861 $ 3,054

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The Company accounts for income taxes under ASC 740. Deferred income tax assets and liabilities are determined based upon differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. The following table provides a reconciliation between income taxes computed at the federal statutory rate and the provision for income taxes (in thousands): Years Ended December 31, 2020 2019 2018 Federal income taxes at 21% for 2020, 2019 and 2018 $ (15,142) $ (8,629) $ (12,393) State income tax, net of federal benefit (469) (1,899) — Tax effect on nondeductible expenses 486 561 (278) Research credits (2,956) (4,141) (4,737) Rate change 344 (664) — Change in valuation allowance 15,912 13,692 16,421 Reserve for uncertain tax positions 739 1,035 1,184 162m deferred tax asset limitation 857 — — Other 229 45 (197) Income tax expense $ — $ — $ — Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2020 2019 Deferred tax assets: Net operating losses $ 62,238 $ 47,468 Research credits 19,330 17,113 Intangibles 221 270 Stock compensation 2,007 2,916 Lease liability 224 458 Other 795 895 Total deferred tax assets 84,815 69,120 Less valuation allowance (84,608) (68,695) Deferred tax assets, net of valuation allowance 207 425 Deferred tax liabilities: Right-of-use assets (207) (425) Total deferred tax liabilities (207) (425) Net deferred tax assets $ — $ — At December 31, 2020, the Company had federal and state net operating loss carryforwards of approximately $282.7 million and $222.1 million, respectively. The federal and state loss carryforwards begin to expire in 2033 and 2029, respectively, unless previously utilized. The Company also has federal research and development and orphan drug credit carryforwards totaling $22.9 million and state research and development credit carryforwards totaling $3.8 million. The federal research and development credit and orphan drug credit carryforwards begin to expire in 2033, unless previously utilized. The state research and development credit carryforwards of $3.8 million have no expiration date. Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use the existing deferred tax assets. Based on the weight of all evidence, including a history of operating losses, management has determined that it is more likely than not that the net deferred tax assets will not be realized. A valuation allowance of $84.6 million and $68.7 million as of December 31, 2020 and 2019, respectively, has been established to offset the net deferred tax assets as realization of such assets is uncertain. Future utilization of the Company’s net operating loss and research and development credit carryforwards to offset future taxable income may be subject to an annual limitation, pursuant to Internal Revenue Code (IRC) Sections 382 and 383, as a result of ownership changes that may have occurred or that could occur in the future. An ownership change occurs when a cumulative change in ownership of more than 50% occurs within a three-year period. The Company has not completed an IRC Section 382/383 analysis regarding the limitation of net operating loss and research and development credit carryforwards. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) was enacted and signed into law in response to coronavirus disease 2019 (“COVID-19”). The CARES Act, among other things, included several significant provisions that impacted corporate taxpayers’ accounting for income taxes. Prior to the enactment of the CARES Act, the 2017 Tax Cuts and Jobs Act generally eliminated the ability to carryback net operating losses (“NOLs”), and permitted the NOLs arising in tax years beginning after December 31, 2017 to be carried forward indefinitely, limited to 80% of the taxpayer’s income. The CARES Act amended the NOL rules, suspending the 80% limitation on the utilization of NOLs generated after December 31, 2017 and before January 1, 2021. Additionally, the CARES Act allows corporate NOLs arising in taxable years beginning after December 31, 2017 and before January 1, 2021, to be carried back to each of the five taxable years preceding the taxable year of the loss. Also, the CARES Act allows companies to defer making certain payroll tax payments until future years. With the enactment of the CARES Act, the company does not expect a financial statement impact from income taxes. The Company recognizes a tax benefit from an uncertain tax position when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. Income tax positions must meet a more likely than not recognition at the effective date to be recognized. At December 31, 2020, 2019 and 2018, the unrecognized tax benefits recorded were approximately $23.3 million, $22.6 million and $16.5 million, respectively. Approximately $19.1 million of the unrecognized tax benefits would reduce the Company's annual effective tax rates, if recognized, subject to the valuation allowances. The Company does not anticipate a significant change in the unrecognized tax benefits within the next 12 months. A reconciliation of the beginning and ending amount of gross unrecognized tax benefits for 2020, 2019 and 2018 is as follows (in thousands): Years Ended December 31, 2020 2019 2018 Balance as of the beginning of the year $ 22,558 $ 16,524 $ 10,756 Increases related to current year tax positions 777 1,074 1,224 Increases related to prior year tax positions — 4,960 4,544 Balance as of the end of the year $ 23,335 $ 22,558 $ 16,524 The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by the United States and state jurisdictions where applicable. There are currently no pending income tax examinations. The Company’s tax years from inception in 2013 are subject to examination by the federal and state tax authorities due to the carryforward of unutilized net operating losses and research and development credits. The Company’s practice is to recognize interest and penalties related to income tax matters in income tax expense. The Company has not recognized interest or penalties since inception.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Litigation —From time to time, the Company may be involved in various lawsuits, legal proceedings, or claims that arise in the ordinary course of business. Management believes there are no claims or actions pending against the Company at December 31, 2020 which will have, individually or in the aggregate, a material adverse effect on its business, liquidity, financial position or results of operations. Litigation, however, is subject to inherent uncertainties, and an adverse result in such matters may arise from time to time that may harm the Company’s business. Lease Obligations —The Company adopted ASU 2016-02, "Leases," on January 1, 2019, which resulted in the recognition of operating leases on the balance sheet. The Company determines if a contract contains a lease at inception and recognizes operating lease right-of-use assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As the Company's leases do not provide an implicit rate, management develops incremental borrowing rates based on the information available at the commencement date in determining the present value of future payments. Lease agreements that have lease and non-lease components are accounted for as a single lease component. Lease expense is recognized on a straight-line basis over the lease term. The Company's single lease upon adoption is for laboratory and office space in San Diego, California and was entered into in June 2014. Amendments for additional space were entered into in February 2015, March 2015 and August 2015. On June 29, 2018 the Company entered into a Fourth Amendment to its lease which extended the term of the lease by an additional 36 months and increases base rent to $70,000 per month effective January 1, 2019. The Company was also granted an option, exercisable prior to September 30, 2019, to expand its leased premises on the same terms as the current lease, subject to compliance with specified conditions. The Company did not exercise this option prior to expiration. The lease expires in December 2021 with options for two individual two The following table presents information about the amount, timing and uncertainty of cash flows arising from the Company's operating lease as of December 31, 2020 (in thousands): 2021 $ 995 Total undiscounted operating lease payments 995 Less: Imputed interest (56) Present value of lease payments $ 939 The balance sheet classification of the Company's operating lease is as follows (in thousands): Balance Sheet Classification: Operating lease right-of-use asset $ 868 Current portion of lease liability $ 939 Total operating lease liability $ 939 As of December 31, 2020, the weighted average remaining lease term was 1 year. Cash paid for amounts included in the present value of operating lease liabilities was $1.0 million for the year ended December 31, 2020. Operating lease costs were $1.0 million, $1.0 million and $0.8 million for the years ended December 31, 2020, 2019 and 2018, respectively. These costs are primarily related to the Company's long-term operating lease, but also include immaterial amounts for variable leases and short-term leases with terms greater than 30 days. Contractual Obligations —The Company enters into contracts in the normal course of business with vendors for research and development activities, manufacturing, and professional services. These contracts generally provide for termination either on notice or after a notice period.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS "At-the-market" offering —In September 2019, the Company began to sell shares of common stock under a controlled equity offering sales agreement with Cantor Fitzgerald & Co. During the period from January 1, 2021, through February 18, 2021, the Company sold 3,132,706 shares of common stock for net proceeds of approximately $8.1 million after deducting placement agent fees.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses and negative cash flows from operating activities since its inception. At December 31, 2020, the Company had an accumulated deficit of $334.7 million. The Company expects to continue to incur net losses into the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. At December 31, 2020, the Company had cash, cash equivalents and restricted cash of $42.9 million. Based on the Company’s current business plan, management believes that existing cash and cash equivalents will not be sufficient to fund the Company’s obligations for twelve months from the issuance of these financial statements. The Company’s ability to execute its operating plan depends on its ability to obtain additional funding through equity offerings, debt financings or potential licensing and collaboration arrangements. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, the Company’s current working capital, anticipated operating expenses and net losses and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, raise substantial doubt about its ability to continue as a going concern for a period of one year following the date that these financial statements are issued. The consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through cash and cash equivalents on hand, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements. There can be no assurance that additional funds will be available when needed from any source or, if available, will be available on terms that are acceptable to the Company. Even if the Company raises additional capital, it may also be required to modify, delay or abandon some of its plans which could have a material adverse effect on the Company’s business, operating results and financial condition and the Company’s ability to achieve its intended business objectives. Any of these actions could materially harm the Company’s business, results of operations and future prospects. In addition to the foregoing, the Company is closely monitoring the impact of the COVID-19 pandemic on its business and has taken steps designed to protect the health and safety of its employees while continuing its operations. Given the level of uncertainty regarding the duration and impact of the COVID-19 pandemic on capital markets and the United States economy, the Company is currently unable to assess the impact of the COVID-19 pandemic on its future access to capital. The Company is continuing to monitor the spread of COVID-19 and its potential impact on the Company's operations. The full extent to which the COVID-19 pandemic will impact the Company's business, results of operations, financial condition, clinical trials, and preclinical research will depend on future developments that are highly uncertain, including actions taken to contain or treat COVID-19 and their effectiveness, as well as the economic impact on national and international markets.
Basis of Consolidation	Basis of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. The Company evaluates its estimates and assumptions on an ongoing basis. The most significant estimates in the Company’s consolidated financial statements relate to estimating the fair value of the Company’s stock options, estimated collaboration expenses and incurred expenses related to the Mundipharma Collaboration Agreement, the fair value of the Company's contingent forward purchase obligations, and certain accruals, including those related to nonclinical and clinical activities. Although the estimates are based on the Company’s knowledge of current events, comparable companies, and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Segment Information	Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all short-term investments purchased with a maturity of three months or less when acquired to be cash equivalents. Restricted cash represents cash that the Company is required to maintain on hand in order to maintain compliance with an operating covenant in the Third Amendment to the Company's Loan Agreement with Pacific Western Bank. See Note 5 for additional information.
Accounts Receivable	Accounts Receivable Accounts receivable are recorded at their net invoice value and are not interest bearing. We reserve specific receivables when collectibility is no longer probable. These reserves are re-evaluated on a regular basis and are adjusted, as needed. Once a receivable is deemed to be uncollectible, such balance is recorded as an allowance for credit losses. No such allowance existed at December 31, 2020 or 2019.
Property and Equipment	Property and Equipment The Company records property and equipment at cost, which consists of lab equipment, computer equipment and software, office equipment, furniture and fixtures and leasehold improvements. Property and equipment is depreciated using the straight-line method over the estimated useful lives (generally three
Concentration of Credit Risk	Concentration of Credit Risk The Company’s financial instruments that are exposed to concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in government insured financial institutions in excess of government insured limits. The Company invests its cash balances in financial institutions that it believes have high credit quality, has not experienced any losses on such accounts and does not believe it is exposed to significant credit risk.
Patent Costs	Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying statements of operations and comprehensive loss.
Income Taxes	Income Taxes The Company follows the Financial Accounting Standards Board, or FASB, Accounting Standards Codification , or ASC, 740, Income Taxes , or ASC 740, in reporting deferred income taxes. ASC 740 requires a company to recognize deferred tax assets and liabilities for expected future income tax consequences of events that have been recognized in the Company’s consolidated financial statements. Under this method, deferred tax assets and liabilities are determined based on temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates in the years in which the temporary differences are expected to reverse. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions pursuant to ASC 740, which prescribes a recognition threshold and measurement process for financial statement recognition of uncertain tax positions taken or expected to be taken in a tax return. If the tax position meets this threshold, the benefit to be recognized is measured as the tax benefit having the highest likelihood of being realized upon ultimate settlement with the taxing authority. The Company recognizes interest accrued related to unrecognized tax benefits and penalties in the provision for income taxes.
Revenue Recognition	Revenue Recognition The Company recognizes revenue is accordance with ASC Topic 606, Revenue from Contracts with Customers , which applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. In a contract with multiple performance obligations, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation, which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price(s) may include estimates regarding forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. Any change made to estimated progress towards completion of a performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in a contract, the Company recognizes revenues from the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from the allocated transaction price. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue or expense recognition as a change in estimate. At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being reached. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or a collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of milestones that are within its or a collaboration partner’s control, such as operational developmental milestones and any related constraint, and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which will affect collaboration revenues and earnings in the period of adjustment. Revisions to the Company’s estimate of the transaction price may also result in negative collaboration revenues and earnings in the period of adjustment. For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, and a license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, the Company has not recognized any royalty revenue from collaborative arrangements. In September 2019, the Company entered into a Collaboration and License Agreement, or the Collaboration Agreement, with Mundipharma Medical Company, or Mundipharma. The Company concluded that there were three significant performance obligations under the Collaboration Agreement: the license, the research and development services, and the clinical supply services, and that the obligations are distinct from each other. Revenue associated with the license was recognized upon delivery in September 2019. The Company concluded that progress towards completion of the research and development and clinical supply performance obligations related to the Collaboration Agreement is best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The Company periodically reviews and updates the estimated collaboration expenses, when appropriate, which may adjust revenue recognized for the period. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in the period could be materially impacted. The transaction price to be recognized as revenue under the Collaboration Agreement consists of the upfront payment and estimated reimbursable research and development and clinical supply costs. Potential future payments for variable consideration, such as clinical, regulatory or commercial milestones, will be recognized when it is probable that, if recorded, a significant reversal will not take place. Potential future royalty payments will be recorded as revenue when the associated sales occur. See Note 8 for additional information.
Research and Development and Grant Funding Costs	Research and Development Costs Research and development expenses consist of wages, benefits and stock-based compensation charges for research and development employees, scientific consultant fees, facilities and overhead expenses, laboratory supplies, manufacturing expenses, and nonclinical and clinical trial costs. The Company accrues nonclinical and clinical trial expenses based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies, and other events. Costs incurred in purchasing technology assets and intellectual property are charged to research and development expense if the technology has not been conclusively proven to be feasible and has no alternative future use. Grant Funding The Company has evaluated the terms of research and development grants to assess its obligations and the classification of funding received. Amounts billable for funded research and development are recognized in the statement of operations as a reduction to research and development expense over the grant period as the related costs are incurred to meet the Company's obligations. The Company recognized immaterial amounts as reductions to research and development expense due to funded grants for the years ended December 31, 2020, 2019 and 2018.
Preclinical and Clinical Trial Accruals	Preclinical and Clinical Trial Accruals The Company makes estimates of its accrued expenses as of each balance sheet date in the financial statements based on the facts and circumstances known at that time. Accrued expenses for preclinical studies and clinical trials are based on estimates of costs incurred and fees that may be associated with services provided by contract research organizations, or CROs, clinical trial investigational sites and other clinical trial-related activities. Payments under certain contracts with such parties depend on factors such as successful enrollment of patients, site initiation and the completion of clinical trial milestones. In accruing for these services, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If possible, the Company obtains information regarding unbilled services directly from these service providers. However, the Company may be required to estimate these services based on other available information. If the Company underestimates or overestimates the activities or fees associated with a study or service at a given point in time, adjustments to research and development expenses may be necessary in future
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity during a period from transactions and other events and/or circumstances from non-owner sources. The Company’s only component of other comprehensive loss is unrealized gains on short-term investments. Comprehensive losses have been reflected in the consolidated statements of operations and comprehensive loss and as a separate component of the consolidated statements of convertible preferred stock and stockholders’ equity for all periods presented.
Stock-based Compensation	Stock-based Compensation The Company accounts for stock-based compensation expense related to employee stock options, restricted stock and employee stock purchase plan rights by estimating the fair value on the date of grant. The Company estimates the fair value of stock option awards to employees and non-employees using the Black-Scholes option pricing model, which requires the input of highly subjective assumptions, including (a) the risk-free interest rate, (b) the expected volatility of our stock, (c) the expected term of the award, and (d) the expected dividend yield. Due to the lack of an adequate history of a public market for the trading of the Company's common stock and a lack of adequate company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. For these analyses, the Company has selected companies with comparable characteristics, including enterprise value, risk profiles, and position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company computes the historical volatility data using the daily close prices for the selected companies’ shares during the equivalent period of the calculated expected term of our stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its common stock price becomes available. The Company has estimated the expected life of its employee stock options using the “simplified” method, whereby the expected life equals the average of the vesting term and the original contractual term of the option. The risk-free interest rates for periods within the expected life of the option are based on the yields of zero-coupon U.S. treasury securities. The fair value of Restricted Stock Units, or RSUs, and Performance-based RSUs, or PRSUs, granted to employees is estimated based on the closing price of the Company's common stock on the date of grant. For awards subject to time-based vesting conditions, stock-based compensation expense is recognized ratably over the requisite service period of the awards. For awards subject to performance-based vesting conditions, the Company assesses the probability of achievement of the individual milestones under the stock-based awards and recognizes stock-based compensation expense over the implicit service period commencing once the Company believes the performance criteria is probable of achievement. The Company accounts for stock options, RSUs, and PRSUs granted to non-employees using the fair value approach. These stock-based awards are subject to periodic revaluation over their vesting terms. The Company recognizes forfeitures related to stock-based compensation as they occur.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss allocable to common shares by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss allocable to common shares by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of warrants, Series X Convertible Preferred Stock, as well as RSUs, PRSUs and options outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding. Net loss allocable to common shares for the years ended December 31, 2020 and 2018 includes non-cash deemed dividends of $2.8 million and $10.3 million, respectively, resulting from the recognition of beneficial conversion features. See Note 6 for additional information.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company follows ASC 820-10 issued by the FASB with respect to fair value reporting for financial assets and liabilities. The guidance defines fair value, provides guidance for measuring fair value and requires certain disclosures. The guidance does not apply to measurements related to share-based payments. The guidance discusses valuation techniques such as the market approach (comparable market prices), the income approach (present value of future income or cash flow), and the cost approach (cost to replace the service capacity of an asset or replacement cost). The guidance establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. The Company’s financial instruments consist of cash and cash equivalents, restricted cash, accounts receivable, accounts payable, accrued liabilities, and a term loan. Fair value estimates of these instruments are made at each reporting period end based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. The carrying amount of cash and cash equivalents, restricted cash, accounts receivable, accounts payable, and accrued liabilities are generally considered to be representative of their respective fair values because of the short-term nature of those instruments. The Company believes that the fair value of long-term debt approximates its carrying value.
Recently Issued and Adopted Accounting Standards	Recently Issued Accounting Standards Recently Issued Accounting Standards Not Yet Adopted In December 2019, the FASB issued ASU 2019-12, "Simplifying the Accounting for Income Taxes," which eliminates certain exceptions within ASC 740, Income Taxes, and clarifies other aspects of the current guidance to promote consistency among reporting entities. The updated guidance is effective for interim and annual periods beginning after December 15, 2020. Early adoption is permitted. The Company does not expect the standard to have a material impact on its financial statements upon adoption. In August 2020, the FASB issued ASU 2020-06, "Accounting for Convertible Instruments and Contracts in an Entity's Own Equity," simplifies the accounting for certain convertible instruments by removing the separation models for convertible debt with a cash conversion feature or convertible instruments with a beneficial conversion feature. Additionally, this ASU amends the diluted EPS calculation for convertible instruments by requiring the use of the if-converted method. The treasury stock method is no longer available. Entities may adopt this ASU using either a full or modified retrospective approach, and it is effective for interim and annual reporting periods beginning after December 15, 2021. Early adoption is permitted for interim and annual reporting periods beginning after December 15, 2020. The Company is assessing the impact the adoption of this ASU will have on its financial statements. Recently Adopted Accounting Standards In August 2018, the FASB issued ASU 2018-13, "Changes to the Disclosure Requirements for Fair Value Measurement," which modifies certain disclosure requirements on fair value measurements. The Company adopted ASU 2018-13 effective January 1, 2020. The adoption of this standard did not have a material impact on the Company's financial statements. In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." The updated guidance replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 requires that an entity measure and recognize expected credit losses for financial assets held at amortized cost and replaces the incurred loss impairment methodology in prior GAAP with a methodology that requires consideration of a broader range of information to estimate credit losses, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because doing so would be anti-dilutive (in common stock equivalent shares): December 31, 2020 2019 2018 Common stock warrants 12,517,328 12,517,328 12,517,328 Series X Convertible Preferred stock 10,442,780 5,652,310 4,452,310 Common stock options, RSUs and PRSUs issued and outstanding 6,787,033 5,360,563 4,392,671 Total 29,747,141 23,530,201 21,362,309

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on Recurring Basis	The following tables summarize the Company’s financial instruments measured at fair value on a recurring basis (in thousands): TOTAL LEVEL 1 LEVEL 2 LEVEL 3 December 31, 2020 Assets: Cash and money market accounts $ 35,912 $ 35,912 $ — $ — Restricted cash and money market accounts 7,037 7,037 — — Total assets at fair value $ 42,949 $ 42,949 $ — $ — December 31, 2019 Assets: Cash and money market accounts $ 50,268 $ 50,268 $ — $ — Restricted cash and money market accounts 10,000 10,000 — — Total assets at fair value $ 60,268 $ 60,268 $ — $ —

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consists of the following (in thousands): December 31, 2020 2019 Laboratory equipment $ 2,304 $ 2,104 Leasehold improvements 425 425 Computer hardware and software 404 481 Office equipment 119 119 Furniture and fixtures 142 142 3,394 3,271 Less accumulated depreciation and amortization (3,052) (2,842) Total $ 342 $ 429

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Future Principal Payments Due	As of December 31, 2020, future principal payments due under the Third Amendment of the Term A Loan are as follows (in thousands): Year ended: December 31, 2021 $ 4,444 December 31, 2022 2,593 Total future principal payments due under the Term A Loan $ 7,037

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows (in common stock equivalent shares): December 31, 2020 2019 Common stock warrants 12,517,328 12,517,328 Series X Convertible Preferred stock 10,442,780 5,652,310 Stock options, RSUs and PRSUs issued and outstanding 6,787,033 5,360,563 Authorized for future stock awards 2,813,131 559,898 Awards available under the ESPP 521,986 463,741 Total 33,082,258 24,553,840

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Summary of RSU and PRSU Activity	The following table summarizes RSU and PRSU activity during the year ended December 31, 2020: Number of Weighted Average Grant Date Fair Value Outstanding at December 31, 2019 383,885 $ 3.97 RSUs and PRSUs granted 151,475 2.29 RSUs and PRSUs vested (74,804) 4.18 RSUs and PRSUs canceled (32,321) 5.40 Outstanding at December 31, 2020 428,235 $ 3.55
Schedule of Stock Option Activity	The following table summarizes stock option activity during the year ended December 31, 2020: Number of Weighted Weighted Total Aggregate Outstanding at December 31, 2019 4,976,678 $ 4.37 7.27 $ 3,880 Options granted 1,747,000 2.15 Options exercised (5,411) 2.55 Options canceled (359,469) 7.30 Outstanding at December 31, 2020 6,358,798 $ 3.59 7.04 $ 55 Vested and expected to vest at December 31, 2020 6,358,798 $ 3.59 7.04 $ 55 Exercisable at December 31, 2020 4,160,074 $ 4.21 6.26 $ 31
Summary of Black-Scholes Option Pricing Model Assumptions	The following table summarizes the Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted to employees under our equity incentive plans and the shares purchasable under our 2015 ESPP during the periods presented: For the years ended December 31, 2020 2019 2015 EIP and 2020 IIP Risk-free interest rate 0.30% - 1.66% 1.42% - 2.57% Expected dividend yield 0% 0% Expected volatility 82% - 85% 80% - 82% Expected term (years) 5.27 - 6.08 5.27 - 6.08 2015 ESPP Risk-free interest rate 0.08% - 0.17% 1.55% - 2.42% Expected dividend yield 0% 0% Expected volatility 65% - 105% 67% - 82% Expected term (years) 0.50 - 2.00 0.50 - 2.00
Summary of Stock-Based Compensation Expense	Stock-based compensation expense recognized for restricted shares, RSUs, PRSUs, stock options, and the ESPP has been reported in the statements of operations and comprehensive loss as follows (in thousands): Years ended December 31, 2020 2019 2018 Research and development $ 2,089 $ 2,502 $ 2,676 General and administrative 2,001 2,571 3,034 Total $ 4,090 $ 5,073 $ 5,710

Significant Agreements and Co_2

Significant Agreements and Contracts (Tables)	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Collaborative Agreement Liabilities and Revenues Disaggregated by Timing of Revenue Recognition	The following table presents a summary of the activity in the Company's contract liabilities (recorded as deferred revenue on the balance sheet) during the year ended December 31, 2020 (in thousands): Opening balance, December 31, 2019 $ 9,803 Payments received 16,129 Milestone payment receivable 11,145 Revenue from performance obligations satisfied during reporting period (12,067) Closing balance, December 31, 2020 $ 25,010 Current portion of deferred revenue $ 13,865 Long-term portion of deferred revenue 11,145 Total deferred revenue, December 31, 2020 $ 25,010 The following table presents our contract revenues disaggregated by timing of revenue recognition (in thousands): Years Ended December 31 2020 2019 Point in Time Over Time Point in Time Over Time Revenue from Mundipharma Collaboration Agreement: License of Intellectual Property $ — $ — $ 17,861 $ — Research and Development Services — 10,513 — 2,670 Clinical Supply Services — 1,554 — 384 Total revenue from Mundipharma Collaboration Agreement $ — $ 12,067 $ 17,861 $ 3,054

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Reconciliation Between Federal Statutory and Provision For Income Taxes	The following table provides a reconciliation between income taxes computed at the federal statutory rate and the provision for income taxes (in thousands): Years Ended December 31, 2020 2019 2018 Federal income taxes at 21% for 2020, 2019 and 2018 $ (15,142) $ (8,629) $ (12,393) State income tax, net of federal benefit (469) (1,899) — Tax effect on nondeductible expenses 486 561 (278) Research credits (2,956) (4,141) (4,737) Rate change 344 (664) — Change in valuation allowance 15,912 13,692 16,421 Reserve for uncertain tax positions 739 1,035 1,184 162m deferred tax asset limitation 857 — — Other 229 45 (197) Income tax expense $ — $ — $ —
Schedule of Components of Net Deferred Tax Assets	Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2020 2019 Deferred tax assets: Net operating losses $ 62,238 $ 47,468 Research credits 19,330 17,113 Intangibles 221 270 Stock compensation 2,007 2,916 Lease liability 224 458 Other 795 895 Total deferred tax assets 84,815 69,120 Less valuation allowance (84,608) (68,695) Deferred tax assets, net of valuation allowance 207 425 Deferred tax liabilities: Right-of-use assets (207) (425) Total deferred tax liabilities (207) (425) Net deferred tax assets $ — $ —
Schedule of Reconciliation Amount of Gross Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of gross unrecognized tax benefits for 2020, 2019 and 2018 is as follows (in thousands): Years Ended December 31, 2020 2019 2018 Balance as of the beginning of the year $ 22,558 $ 16,524 $ 10,756 Increases related to current year tax positions 777 1,074 1,224 Increases related to prior year tax positions — 4,960 4,544 Balance as of the end of the year $ 23,335 $ 22,558 $ 16,524

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of Amount, Timing and Uncertainty of Cash Flows from Operating Lease	The following table presents information about the amount, timing and uncertainty of cash flows arising from the Company's operating lease as of December 31, 2020 (in thousands): 2021 $ 995 Total undiscounted operating lease payments 995 Less: Imputed interest (56) Present value of lease payments $ 939
Supplemental Balance Sheet Information	The balance sheet classification of the Company's operating lease is as follows (in thousands): Balance Sheet Classification: Operating lease right-of-use asset $ 868 Current portion of lease liability $ 939 Total operating lease liability $ 939

The Company and Basis of Pres_2

The Company and Basis of Presentation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 334,700	$ 259,827
Cash, cash equivalents and restricted cash	$ 42,949	$ 60,268	$ 74,562	$ 60,813
Number of operating segments | segment	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Recognition of beneficial conversion feature	$ 0	$ 0
Additional Paid-In Capital
Property, Plant and Equipment [Line Items]
Recognition of beneficial conversion feature	$ 2,762	$ 10,329
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful lives	7 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	29,747,141	23,530,201	21,362,309
Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	12,517,328	12,517,328	12,517,328
Series X Convertible Preferred stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	10,442,780	5,652,310	4,452,310
Common stock options, RSUs and PRSUs issued and outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in the calculation of diluted net loss per share (in shares)	6,787,033	5,360,563	4,392,671

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	May 21, 2018USD ($)closing	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	$ 4,300,000
Change in fair value of contingent forward purchase obligation		$ 0	$ 411,000	$ 3,851,000
Registered Direct Offering
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Aggregate value of shares authorized to be sold	$ 120,000,000
Number of direct offering closings | closing	3

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Cash and money market accounts	$ 35,912	$ 50,268
Restricted cash and money market accounts	7,037	10,000
Assets at fair value	42,949	60,268
LEVEL 1
Assets:
Cash and money market accounts	35,912	50,268
Restricted cash and money market accounts	7,037	10,000
Assets at fair value	42,949	60,268
LEVEL 2
Assets:
Cash and money market accounts	0	0
Restricted cash and money market accounts	0	0
Assets at fair value	0	0
LEVEL 3
Assets:
Cash and money market accounts	0	0
Restricted cash and money market accounts	0	0
Assets at fair value	$ 0	$ 0

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,394	$ 3,271
Less accumulated depreciation and amortization	(3,052)	(2,842)
Total	342	429
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,304	2,104
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	425	425
Computer hardware and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	404	481
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	119	119
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 142	$ 142

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation and amortization of property and equipment	$ 286	$ 328	$ 523

Debt - Additional Information (

Debt - Additional Information (Details) - USD ($)	Jul. 27, 2018	Oct. 03, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Shares of common stock issued upon exercise of warrant (in shares)		17,331
Warrants weighted average exercise price (USD per share)		$ 11.54
Percentage of principal of debt used to calculate number of shares issued by warrant		2.00%
Period of average closing price used to calculate number of shares issued by warrant		30 days
Warrant term		10 years
Restricted cash			$ 7,037,000	$ 10,000,000
Term Loan | Loan Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 20,000,000
Prepayment fee percentage in year one		2.00%
Prepayment fee percentage in year two		1.00%
Stated interest rate	4.50%		4.50%
Term Loan | Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.75%
Term Loan | Term A Loan
Debt Instrument [Line Items]
Debt face amount		$ 10,000,000
Interest expense for the amortization of the fair value of warrants and debt issue costs			$ (21,000)	$ (36,000)	$ (56,000)
Term Loan | Term B Loan
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 10,000,000

Debt - Schedule of Future Princ

Debt - Schedule of Future Principal Payments Due (Details) - Term Loan - Term A Loan $ in Thousands	Dec. 31, 2020USD ($)
Year ended:
December 31, 2021	$ 4,444
December 31, 2022	2,593
Total future principal payments due under the Term A Loan	$ 7,037

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	Aug. 12, 2020shares	Feb. 12, 2020USD ($)$ / sharesshares	Sep. 03, 2019USD ($)day$ / sharesshares	Mar. 22, 2019shares	May 23, 2018USD ($)$ / sharesshares	May 21, 2018USD ($)closingday$ / shares	May 31, 2018$ / sharesshares	Dec. 31, 2020USD ($)vote_per_share$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)shares	Oct. 03, 2016$ / shares
Class of Stock [Line Items]
Dividends, preferred stock | $								$ 0		$ 0
Recognition of beneficial conversion feature | $					$ 10,300,000			$ 2,762,000	$ 0	10,329,000
Share price allowing the reduction of the aggregate offering size (USD per share) | $ / shares						$ 6.81
Preferred stock, shares authorized (in shares)								10,000,000	10,000,000
Preferred stock, par value (USD per share) | $ / shares								$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)								200,000,000	200,000,000
Number of votes for each share held | vote_per_share								1
Dividends in arrears or default | $								$ 0
Warrants exercise price (USD per share) | $ / shares											$ 11.54
Rights Offering, January 2020
Class of Stock [Line Items]
Net proceeds | $		$ 30,000,000
Preferred units, offering costs | $		800,000
Proceeds from sale of equity | $		$ 29,200,000
Registered direct offering, first closing and First Private Placement
Class of Stock [Line Items]
Net proceeds | $					$ 49,500,000
Controlled Equity Sales Agreement, Cantor Fitzgerald and Company
Class of Stock [Line Items]
Net proceeds | $								$ 11,200,000	$ 5,300,000	$ 6,400,000
Shares sold (in shares)								3,515,871	2,095,887	847,937
Registered Direct Offering
Class of Stock [Line Items]
Aggregate value of shares authorized to be sold | $						$ 120,000,000
Number of direct offering closings | closing						3
Registered direct offering, first closing
Class of Stock [Line Items]
Shares sold (in shares)					6,185,987
Offering price (USD per share) | $ / shares					$ 4.70
Registered direct offering, second closing
Class of Stock [Line Items]
Offering price (USD per share) | $ / shares						$ 4.70
Threshold trading days | day						5
Registered direct offering, third closing
Class of Stock [Line Items]
Offering price (USD per share) | $ / shares						$ 4.70
Option fee paid by investors relating to third closing | $					$ 500,000
Warrant | First Private Placement
Class of Stock [Line Items]
Shares sold (in shares)					12,499,997
Offering price (USD per share) | $ / shares					$ 0.125
Series X Convertible Preferred Stock
Class of Stock [Line Items]
Beneficial conversion feature fair value | $					$ 10,300,000
Preferred stock, shares authorized (in shares)							5,000,000	5,000,000	5,000,000
Preferred stock, par value (USD per share) | $ / shares							$ 0.0001	$ 0.0001	$ 0.0001
Conversion of stock, shares issued (in shares)				120,000
Issuance of Series X Convertible Preferred Stock in exchange for common stock (in shares)	52,241							(52,241)	120,000
Common stock issued for each preferred stock (in shares)							10
Maximum ownership following conversion							9.99%
Series X Convertible Preferred Stock | Rights Offering, January 2020
Class of Stock [Line Items]
Shares sold (in shares)		531,288
Offering price (USD per share) | $ / shares		$ 25.10
Dividends, preferred stock | $		$ 2,800,000
Series X Convertible Preferred Stock | Registered direct offering, first closing
Class of Stock [Line Items]
Shares sold (in shares)					445,231
Offering price (USD per share) | $ / shares					$ 47
Common Stock
Class of Stock [Line Items]
Conversion of stock, shares converted (in shares)				1,200,000
Common Stock | Rights Offering, January 2020
Class of Stock [Line Items]
Shares sold (in shares)		6,639,307
Offering price (USD per share) | $ / shares		$ 2.51
Common Stock | Stock Purchase Agreement
Class of Stock [Line Items]
Net proceeds | $			$ 9,000,000
Shares sold (in shares)			4,781,408
Offering price (USD per share) | $ / shares			$ 1.884
Premium percentage on volume weighted average price per share			20.00%
Threshold trading days | day			10
Common Stock
Class of Stock [Line Items]
Issuance of Series X Convertible Preferred Stock in exchange for common stock (in shares)	522,410							522,410	(1,200,000)
Common Stock Warrant
Class of Stock [Line Items]
Outstanding warrants to purchase common stock (in shares)								12,517,328	12,517,328
Outstanding warrants to purchase common stock, intrinsic value | $								$ 0	$ 0
Common Stock Warrant | Weighted Average
Class of Stock [Line Items]
Warrants exercise price (USD per share) | $ / shares								$ 6.82	$ 6.82

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Total (in shares)	33,082,258	24,553,840
Warrant
Class of Stock [Line Items]
Total (in shares)	12,517,328	12,517,328
Series X Convertible Preferred Stock
Class of Stock [Line Items]
Total (in shares)	10,442,780	5,652,310
Stock options, RSUs and PRSUs issued and outstanding
Class of Stock [Line Items]
Total (in shares)	6,787,033	5,360,563
Authorized for future stock awards
Class of Stock [Line Items]
Total (in shares)	2,813,131	559,898
Awards available under the ESPP
Class of Stock [Line Items]
Total (in shares)	521,986	463,741

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) $ / shares in Units, $ in Millions	Dec. 18, 2019USD ($)$ / sharesshares	Nov. 20, 2019$ / shares	Mar. 31, 2015shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible common stock for purchase in the option exchange, exercise price minimum (USD per share) | $ / shares		$ 2.28
Eligible common stock for purchase in the option exchange (in shares) | shares	1,656,379
Percentage of eligible common stock for purchase in the option exchange	60.40%
New option to purchase common stock in the option exchange (in shares) | shares	1,529,814
New option to purchase common stock, exercise price, in the option exchange (USD per share) | $ / shares	$ 2.45
Incremental compensation expense in the option exchange	$ 0.7
Weighted average grant date fair values of stock options granted (USD per share) | $ / shares				$ 1.48	$ 1.78	$ 2.98
Options, exercises in period, intrinsic value						$ 0.2
Unrecognized share-based compensation expense of unvested employee stock options				$ 3.4
Unvested stock options, unrecognized cost expected to be recognized				1 year 10 months 20 days
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Automatic annual increase in shares authorized for issuance in equity incentive plan			1.00%
Price of stock option as percentage of estimated fair value of shares on date of grant			85.00%
Employee payroll deduction under the stock plan			15.00%
Issuance of common stock under employee stock purchase plan (in shares) | shares				280,139	242,501	158,066
Unrecognized share-based compensation expense of unvested employee stock options				$ 0.1
Unvested stock options, unrecognized cost expected to be recognized				6 months 25 days
RSUs and PRSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share) | $ / shares				$ 2.29	$ 2.88	$ 3.83
Vested in period, fair value				$ 0.3	$ 0.5
Unrecognized share-based compensation expense of unvested employee stock options				$ 1.3
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		7 years
Minimum | Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Maximum | 2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares outstanding (in shares) | shares			490,336
Maximum | Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
2015 EIP and 2020 IIP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Automatic annual increase in shares authorized for issuance in equity incentive plan			4.00%
Expiration period			10 years
Price of stock option as percentage of estimated fair value of shares on date of grant			100.00%
Employee voting power, percentage (more than)			10.00%
2015 EIP and 2020 IIP | More than 10% of voting power
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price of stock option as percentage of estimated fair value of shares on date of grant			110.00%
2015 EIP and 2020 IIP | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
2015 EIP and 2020 IIP | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Non Section 16 Officer, Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option exchange, exchange ratio		1
Section 16 Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option exchange, exchange ratio		1.5

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of RSU and PRSU Activity (Details) - RSUs and PRSUs - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of RSUs and PRSUs
Outstanding, beginning of period (in shares)	383,885
Granted (in shares)	151,475
Vested (in shares)	(74,804)
Canceled (in shares)	(32,321)
Outstanding, end of period (in shares)	428,235	383,885
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share)	$ 3.97
Granted (in dollars per share)	2.29	$ 2.88	$ 3.83
Vested (in dollars per share)	4.18
Granted (in dollars per share)	5.40
Outstanding, end of period (in dollars per share)	$ 3.55	$ 3.97

Equity Incentive Plans - Summ_2

Equity Incentive Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Beginning balance (in shares)	4,976,678
Granted (in shares)	1,747,000
Exercised (in shares)	(5,411)
Canceled (in shares)	(359,469)
Ending balance (in shares)	6,358,798	4,976,678
Vested and expected to vest (in shares)	6,358,798
Exercisable (in shares)	4,160,074
Weighted Average Exercise Price
Beginning balance (USD per share)	$ 4.37
Granted (USD per share)	2.15
Exercised (USD per share)	2.55
Canceled (USD per share)	7.30
Ending balance (USD per share)	3.59	$ 4.37
Vested and expected to vest (USD per share)	3.59
Exercisable (USD per share)	$ 4.21
Weighted Average Remaining Contractual Life in Years
Weighted Average Remaining Contractual Term	7 years 14 days	7 years 3 months 7 days
Weighted Average Remaining Contractual Term, Vested and expected to vest	7 years 14 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 3 months 3 days
Total Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value, beginning balance	$ 3,880
Aggregate Intrinsic Value, ending balance	55	$ 3,880
Aggregate Intrinsic Value, Vested and expected to vest	55
Aggregate Intrinsic Value, Exercisable	$ 31

Equity Incentive Plans - Summ_3

Equity Incentive Plans - Summary of Black-Scholes Option Pricing Model Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	0.08%	1.55%
Risk-free interest rate, maximum	0.17%	2.42%
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum	65.00%	67.00%
Expected volatility, maximum	105.00%	82.00%
2015 Employee Stock Purchase Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months
2015 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	2 years	2 years
2015 EIP and 2020 IIP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	0.30%	1.42%
Risk-free interest rate, maximum	1.66%	2.57%
Expected dividend yield	0.00%	0.00%
Expected volatility, minimum	82.00%	80.00%
Expected volatility, maximum	85.00%	82.00%
2015 EIP and 2020 IIP | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 7 days	5 years 3 months 7 days
2015 EIP and 2020 IIP | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days

Equity Incentive Plans - Summ_4

Equity Incentive Plans - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 4,090	$ 5,073	$ 5,710
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,089	2,502	2,676
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,001	$ 2,571	$ 3,034

Significant Agreements and Co_3

Significant Agreements and Contracts - Additional Information (Details) - USD ($)	Sep. 03, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2020	Sep. 30, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Long-term deferred revenue		$ 11,145,000	$ 0
Revenue from collaborative agreement		12,067,000	20,915,000	$ 0
Mundipharma Medical Company
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative agreement, maximum cost share, percentage	50.00%
Affiliated Entity | Mundipharma Medical Company
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative agreement, maximum cost share	$ 31,200,000
Collaborative agreement, potential transaction value	568,000,000
Payments related to collaborative agreement	30,000,000
Revenue recognized from collaborative agreement related to performance obligation satisfied at a point in time		0	17,861,000
Affiliated Entity | Mundipharma Medical Company | License of Intellectual Property
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized from collaborative agreement related to performance obligation satisfied at a point in time		0	17,861,000			$ 17,900,000
Long-term deferred revenue					$ 11,100,000
Affiliated Entity | Mundipharma Medical Company | Milestone Achievement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from collaborative agreement		0	0	0
Affiliated Entity | Mundipharma Medical Company | Royalty
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from collaborative agreement		$ 0	$ 0	$ 0
Affiliated Entity | Near Term Milestone | Mundipharma Medical Company
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement, additional third party funding commitment	$ 11,100,000

Significant Agreements and Co_4

Significant Agreements and Contracts - Summary of Contract Liability Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Revenue From Collaborative Arrangement, Excluding Revenue From Contract With Customer, Liability [Roll Forward]
Closing balance	$ 25,010
Current deferred revenue		$ 13,865	$ 9,803
Long-term deferred revenue		11,145	0
Total deferred revenue, December 31, 2020	25,010	25,010
Affiliated Entity | Mundipharma Medical Company
Revenue From Collaborative Arrangement, Excluding Revenue From Contract With Customer, Liability [Roll Forward]
Opening balance	9,803
Payments received	16,129
Milestone payment receivable	11,145
Revenue from performance obligations satisfied during reporting period	(12,067)
Closing balance	25,010
Total deferred revenue, December 31, 2020	$ 25,010	$ 25,010	$ 9,803

Significant Agreements and Co_5

Significant Agreements and Contracts - Revenues Disaggregated by Timing of Revenue Recognition (Details) - Affiliated Entity - Mundipharma Medical Company - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from Mundipharma Collaboration Agreement, Point in Time	$ 0	$ 17,861
Revenue from Mundipharma Collaboration Agreement, Over Time	12,067	3,054
Research and Development Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from Mundipharma Collaboration Agreement, Over Time	10,513	2,670
Clinical Supply Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from Mundipharma Collaboration Agreement, Over Time	1,554	384
License of Intellectual Property
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue from Mundipharma Collaboration Agreement, Point in Time	$ 0	$ 17,861	$ 17,900

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Income Taxes Computed at Federal Statutory Rate and Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal income taxes at 21% for 2020, 2019 and 2018	$ (15,142)	$ (8,629)	$ (12,393)
State income tax, net of federal benefit	(469)	(1,899)	0
Tax effect on nondeductible expenses	486	561	(278)
Research credits	(2,956)	(4,141)	(4,737)
Rate change	344	(664)	0
Change in valuation allowance	15,912	13,692	16,421
Reserve for uncertain tax positions	739	1,035	1,184
162m deferred tax asset limitation	857	0	0
Other	229	45	(197)
Income tax expense	$ 0	$ 0	$ 0

Income Taxes - Significant Comp

Income Taxes - Significant Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating losses	$ 62,238	$ 47,468
Research credits	19,330	17,113
Intangibles	221	270
Stock compensation	2,007	2,916
Lease liability	224	458
Other	795	895
Total deferred tax assets	84,815	69,120
Less valuation allowance	(84,608)	(68,695)
Deferred tax assets, net of valuation allowance	207	425
Deferred tax liabilities:
Right-of-use assets	(207)	(425)
Total deferred tax liabilities	207	425
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Research and development credit carryforwards, no subject to expiration	$ 3,800
Deferred tax assets, valuation allowance	84,608	$ 68,695
Unrecognized tax benefits	23,335	$ 22,558	$ 16,524	$ 10,756
Unrecognized tax benefits that would impact on effective tax rate	19,100
Federal
Income Tax Contingency [Line Items]
Net operating loss carryforwards	282,700
Tax credit carryforwards, research and development	22,900
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards	222,100
Tax credit carryforwards, research and development	$ 3,800

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Unrecognized tax benefits
Balance as of the beginning of the year	$ 22,558	$ 16,524
Increases related to current year tax positions	777	1,074	$ 1,224
Increases related to prior year tax positions	0	4,960	4,544
Balance as of the end of the year	$ 23,335	$ 22,558	$ 10,756

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Jan. 01, 2019USD ($)	Dec. 31, 2020USD ($)claim1extension	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of claims and actions pending | claim1		0
Operating leases renewal term	36 months
Base rent	$ 70,000
Number of operating lease options for extension | extension		2
Term of extension		2 years
Annual increase in base rent		3.00%
Adjusted incremental borrowing rate used in measuring lease liability		10.80%
Weighted average remaining lease term		1 year
Cash paid for present value of operating lease liabilities		$ 1,000,000
Lease rent expense		$ 1,000,000	$ 1,000,000
Lease rent expense				$ 800,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Amount, Timing and Uncertainty of Cash Flows from Operating Lease (Details) $ in Thousands	Dec. 31, 2020USD ($)
Commitments and Contingencies Disclosure [Abstract]
2021	$ 995
Total undiscounted operating lease payments	995
Less: Imputed interest	(56)
Present value of lease payments	$ 939

Commitments and Contingencies_3

Commitments and Contingencies - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Operating lease right-of-use asset	$ 868	$ 1,632
Current portion of lease liability	939	$ 818
Total operating lease liability	$ 939

Subsequent Events (Details)

Subsequent Events (Details) - At-The-Market Offering - Subsequent event $ in Millions	2 Months Ended
	Feb. 18, 2021USD ($)shares
Subsequent Event [Line Items]
Shares sold (in shares) | shares	3,132,706
Net proceeds | $	$ 8.1